Chemistry (IB/A-level/AP & first-year uni) — clear, step-by-step lessons with a Chemistry BSc tutor

From 38 C$ /h

Chemistry can be challenging if it’s taught as pure memorization — my goal is to change that. With over 5 years of tutoring experience and a BSc in Chemistry from TU/e, I help students understand the “why” and “how” behind chemistry, turning tricky concepts into something logical and even enjoyable.

This class is for high school students (IB SL/HL, A-level, AP) and first-year university students taking General Chemistry. Lessons are in English and are ideal for international students or anyone who prefers studying in English.

We cover all major topics, including stoichiometry and moles, thermodynamics, equilibrium, acids, bases and buffers, kinetics, electrochemistry, atomic structure, bonding, and organic chemistry basics (nomenclature, mechanisms, isomerism).

A typical 60-minute lesson includes: 1) quick check-in and goal-setting, 2) a clear explanation with one core example, 3) guided practice with feedback, 4) an exam-style problem under light time pressure, and 5) recap and micro-homework with an error log to track recurring mistakes.

Lessons are available online (interactive whiteboard, past papers, custom notes) or in-person in Eindhoven.

Location

Online from Netherlands

About Me

I’m Valerian, a Chemistry BSc from TU/e. I help high-school and first-year university students master Chemistry, Calculus/Math, and high-school Physics.

My tutoring is clear and structured: I diagnose where understanding breaks down, rebuild concepts step by step, and coach problem-solving so students become confident and independent. I care about efficiency, calm progress, and real understanding—not rote memorization. Lessons are in English, online worldwide. If you want clarity and steady results, I’d be happy to help.

Outside of teaching I love dancing, debating, and cooking — things that keep me curious, communicative, and creative, qualities I bring to every lesson.

Education

Technical University of Eindhoven (TU/e)
BSc Chemistry and Chemical Engineering (Cum Laude)

High School:
“Orizont” Lyceum, Moldova
Member of Chemistry Olympiad team

Experience / Qualifications

Private Tutor (5+ years): chemistry, math/calculus, HS physics; personalised study plans; exam prep; steady, measurable progress.

University Calculus Tutor (TU/e): led groups; emphasised conceptual clarity and exam skills; graded assignments consistently.

Lab Assistant — Introductory Chemistry (TU/e): supervised practicals; taught procedures and safety; linked theory to experiments.

IChO mentoring and awards: Created learning resources for Olympiad peers. Bronze medalist, International Chemistry Olympiad (2021 & 2022).

Age

Teenagers (13-17 years old)

Adults (18-64 years old)

Student level

Beginner

Intermediate

Advanced

Duration

60 minutes

The class is taught in

English

Romanian

Skills

Organic chemistry

Chemistry

Availability of a typical week

(GMT -04:00)

New York

Online via webcam

Mon

Tue

Wed

Thu

Fri

Sat

Sun

00-04

04-08

08-12

12-16

16-20

20-24

Calculus & Math (HS + first-year uni) — limits, derivatives, integrals, and problem-solving strategies

38 C$ /h

Math becomes manageable when you see it step by step. I help students build solid foundations and tackle problems with confidence.

For: high-school (algebra, pre-calculus, IB HL math, A-level math) and first-year university Calculus I–II.

We cover functions and graphs, limits and continuity, derivatives and applications (rates, optimization, curve sketching), integrals and applications (area, volume, accumulation), sequences/series, and basic vectors/linear algebra if required.

A typical 60-minute lesson: 1) short diagnostic to spot weak points, 2) concise concept explanation, 3) guided examples → independent practice, 4) exam-style problem under light time pressure, 5) recap and small next-step plan with an error log to track progress.

Available online (interactive whiteboard, problem banks) .

High-School Physics — mechanics, energy, electricity, waves (IB SL / AP 1 / A-level foundations)

31 C$ /h

Physics gets easier when formulas connect to intuition. I guide students step by step so concepts make sense and problems feel solvable.

For: high-school physics (IB SL, AP Physics 1, A-level foundations) and students preparing for exams or needing a stronger base for university.

We cover kinematics, Newton’s laws, forces and friction, energy and power, momentum and collisions, circular motion, simple harmonic motion and waves, basic electricity and DC circuits.

Lesson structure (60 min): 1) goal-setting and concept overview, 2) worked example, 3) guided practice, 4) short timed problem, 5) recap and next-step plan. Mistakes are logged and revisited to ensure steady improvement.

Lessons online.

Kevin

5.0

(5)

► Online Mathematics, Physics & Chemistry Tutor from Switzerland
► GCSE, IGCSE, A-Level, IB & International School Support
I completed my Master’s degree in Business Information Systems at a Swiss University of Applied Sciences, where my main academic focus was strongly connected to Mathematics, Physics, analytical thinking and problem-solving. This technical background shaped the way I teach today: clearly, logically and with a strong focus on real understanding.
► EXTENSIVE EXPERIENCE WITH GCSE, IGCSE, A-LEVEL, IB & INTERNATIONAL SCHOOL STUDENTS
With many years of teaching experience, I have successfully supported students from prestigious schools and highly demanding academic programmes, helping them strengthen their understanding, master exam techniques and achieve excellent progress in Mathematics, Physics and Chemistry.

► Exam Preparation & Academic Support

► GCSE & IGCSE Mathematics, Physics and Chemistry
I help students build a strong foundation through clear explanations, topic-by-topic revision and carefully selected exam-style practice. My lessons focus on understanding the core ideas, improving calculation skills, avoiding common mistakes and preparing students confidently for their final exams.

► A-Level Mathematics, Further Mathematics, Physics and Chemistry
A-Level subjects require deeper thinking, strong problem-solving ability and excellent exam technique. I support students with advanced concepts, structured revision, challenging practice questions and university preparation, especially for demanding fields such as Engineering, Medicine, Computer Science, Economics and Natural Sciences.

► International Baccalaureate — IB Mathematics, Physics and Chemistry
I provide structured support for both Standard Level and Higher Level students. My focus is on deep conceptual understanding, clear mathematical reasoning, scientific explanation and strong exam performance. Students learn how to approach complex IB-style questions with confidence and precision.

► International School Programmes
I support students following international, bilingual and private school curricula. Since every school can have slightly different expectations, I adapt my teaching to the student’s syllabus, textbook, teacher requirements and exam format, ensuring that the lessons are directly useful for school success.

► University & Foundation Courses
For older students, I offer support in Mathematics, Physics, Chemistry, Statistics and technical modules. I help students understand difficult theory, work through assignments, prepare for exams and strengthen the analytical skills needed for university-level study.

► How I Teach
► I focus on understanding, not memorisation.
I explain concepts step by step until the student truly understands why a method works.
► I adapt every lesson to the student.
Every student learns differently, so I adjust my teaching style, pace and examples individually.
► I simplify difficult topics.
Complex problems become easier when they are broken into clear, logical steps.
► I close knowledge gaps.
I identify missing foundations and rebuild them carefully so the student gains confidence.
► I train exam technique.
Students learn how to read questions properly, avoid common mistakes and solve problems under exam conditions.

► 100% COMMITMENT TO YOUR SUCCESS
With clear guidance, focused practice and a personalized learning strategy, I am fully committed to helping you understand deeply, improve consistently and achieve your strongest possible results.

► My Goal
My goal is not only to improve grades, but to help students become confident, independent and motivated learners. With the right guidance, Mathematics, Physics and Chemistry become clear, logical and much easier to master.
► Subjects: Mathematics, Physics, Chemistry
► Levels: GCSE, IGCSE, A-Level, IB, International School, Foundation Courses, University Modules
► Focus: Understanding, confidence, exam success and long-term academic progress.

Raef

5.0

(5)

I give private lessons at home or online by a very modern method of Mathematics - Analysis - Matrices - Statistics - Algebra - Geometry - Physics - Mechanics - Electricity - Chemistry - Organic Chemistry - Biology, Geology of new French program or International School (in english IB) to students in Terminales, 1ère, Seconde, Brevet, Concours and university preparatory classes or 1st university year.
You can contact me for details.
I practice teaching since I was a student where I was first in my class.
Program and special rate for some countries that finish their program later where I can be there with help to better prepare CNED homework
‎‏The results of my final year students over the last 10 years were with the grades VERY GOOD, GOOD and EXCELLENT.
In this area of Asia, you benefit from reduced rates and a free mini session after booking.
Do not hesitate to contact me for more information, answer in a few minutes up to 12 hours maximum..

Aneeka

5.0

(5)

I am currently a Medical Student and have completed a degree in Biomedical student at Cardiff University. I am warming friendly, willing to help and enthusiastic person. I put all my effort in to something I do. I relish the opportunity to help those who are struggling or who wish to go the extra mile to deepen their knowledge of their chosen subject. f you would like some support for your child im here to help at any age up-to A level
I can provide highly planned, engaging, student-centred lessons that are catered to each individual's needs, and I can be as flexible as you'd like with timings and prefer to go on Skype.

I can provide references. I have previously done work in nurseries and primary schools. I also have taught small children Arabic and religious teachings. I also Have a DBS.

Please don't hesitate to get in touch with me at any time

Amin

5.0

(5)

Struggling with math, physics, or chemistry? You're not alone — these subjects are hard, and classroom explanations are rarely enough.
I offer personalized tutoring for middle school, high school, and early university students following the French Mission curriculum, the Moroccan national curriculum, or the international baccalaureate.
Topics covered:

Mathematics: algebra, geometry, calculus, trigonometry, probability
Physics: mechanics, electricity, optics, thermodynamics
Chemistry: organic, inorganic, stoichiometry, reactions

My approach:
I don't re-explain the textbook — I identify exactly where your understanding breaks down and fix it from there. Each session is built around your specific difficulties, not a preset program.
I completed CPGE (Classes Préparatoires aux Grandes Écoles) in Mathematics and Physics before graduating as a State Engineer — I know these subjects at an advanced level and I know where students typically get lost.
Individual and small group sessions available. Online (worldwide) in French, Arabic, or English.

Magdi

5.0

(5)

AP Chemistry Tutor – Exam Preparation & Advanced Chemistry

Are you preparing for AP Chemistry and looking for a structured tutor who can help you understand difficult concepts, master calculations, and improve your exam performance?

I’m **Dr. Basil Magdi**, a Chemistry and Science tutor with **10+ years of experience teaching international curricula**, including AP, IGCSE, GCSE, A-Level, IB, and American Chemistry. With a background in Pharmacy and extensive Chemistry teaching experience, I provide structured, personalized online lessons designed around each student's level and goals.

My approach combines **conceptual understanding + problem-solving + exam technique**, so students learn not only what to study, but how to apply their knowledge to AP-style questions.

### AP Chemistry – Key Areas

• Atomic structure and periodic trends
• Chemical bonding and molecular structure
• Intermolecular forces
• Stoichiometry and quantitative chemistry
• Thermochemistry and thermodynamics
• Chemical kinetics
• Chemical equilibrium
• Acids, bases, and buffers
• Solubility and equilibrium
• Redox reactions and electrochemistry
• Laboratory concepts and data analysis
• Experimental design and error analysis
• AP-style multiple-choice questions
• Free-response questions (FRQs)
• Exam strategies and time management

### Advanced Organic Chemistry

For students taking university-level or advanced Chemistry:

• Functional groups and nomenclature
• Reaction mechanisms
• Substitution and elimination reactions
• Addition reactions
• Isomerism and stereochemistry
• Reaction pathways
• Organic synthesis

### Advanced Inorganic Chemistry

• Periodic trends and chemical properties
• Transition-metal chemistry
• Coordination compounds
• Redox chemistry
• Inorganic reaction principles
• Industrial chemistry

### What You Can Expect

✓ Clear, step-by-step explanations
✓ Personalized lessons based on your level
✓ Extensive problem-solving practice
✓ AP-style questions and FRQs
✓ Regular assessment of progress
✓ Exam-focused strategies
✓ Support with homework and difficult topics
✓ Online lessons using an interactive teaching approach

Whether your goal is to **build a strong foundation, improve your grades, prepare for the AP Chemistry exam, or master advanced Chemistry**, I can help you develop the knowledge and problem-solving skills needed to succeed.

**Book a lesson and let's build your Chemistry skills step by step.**

Mavi

5.0

(5)

I am Mavi, a physics engineer working at an aerospace company.
I have been teaching private lessons at the primary, secondary, high school, and university preparatory levels for 11 years. I teach mathematics, physics, chemistry, and science. I have a good command of the curricula of IB, IGCSE, American, Hong Kong, and international schools.

Additionally, I hold the position of president at the Astronomy Society, where I foster my students' interest in astronomy and science beyond the lessons. I prepare the learning environment by incorporating experiments and exploration, moving away from rote education. I often bring experimental materials to class, aiming to make learning memorable through hands-on experiments.

As an educational mentor, I approach my students as if they were my siblings, valuing creativity. I have a deep passion for mathematics, physics, and science. I am dedicated to helping students understand and learn because life encompasses both SCIENCE and ART. The more people I can inspire to know, understand, and love mathematics, physics, and chemistry, the more proud I am.

Are you curious about how nature works?

Let's explore together!

Georgio

5.0

(5)

FRENCH longer...

Dear parents, Dear students,

I am writing to express my enthusiasm and commitment to providing private tutoring services in mathematics, physics, chemistry, and science across various levels and educational systems. With a deep passion for these subjects and a dedicated approach to education, my goal is to inspire and guide students toward a deeper understanding and appreciation of these fundamental disciplines.

My long and extensive background in private tutoring has given me a deep understanding and skill in effectively imparting knowledge to students with diverse learning abilities.

Through my tutoring efforts, I strive not only to elucidate complex concepts but also to instill problem-solving skills, critical thinking, and a curiosity-driven approach to learning. I tailor my teaching methodologies to individual learning styles, ensuring that each student achieves a thorough mastery of the subject matter and gains confidence in their academic pursuits.

Additionally, my experience extends beyond classroom teaching. I believe in creating a stimulating environment where students feel empowered to ask questions, participate in discussions, and explore the wonders of science and mathematics.

My ultimate goal as a tutor is to inspire a genuine passion for these subjects while helping students achieve their academic goals. I am committed to providing comprehensive support, personalized guidance, and a rewarding educational experience to every student I work with.

I am confident that my dedication, expertise, and ability to inspire learning will make a significant difference in my students' educational journey. I look forward to the opportunity to contribute to the academic success of those I teach.

I am excited about the prospect of working with students and making a positive impact through private tutoring.

Regards,
Georgio

FRENCH

Dear parents, Dear students,

I am writing to express my enthusiasm and commitment to providing private tutoring services in mathematics, physics, chemistry, and science, spanning various levels and educational systems. With a deep passion for these subjects and a dedicated approach to education, my goal is to inspire and guide students toward a deep understanding and appreciation of these fundamental disciplines.

My long and extensive background in private tutoring has given me a deep understanding and mastery of effectively imparting knowledge to students with diverse learning abilities.

Through my tutoring efforts, I strive not only to explain complex concepts but also to instill problem-solving skills, critical thinking, and a curiosity-based approach to learning. I customize my teaching methods to match individual learning styles, ensuring that each student fully grasps the material and gains confidence in their studies.

Furthermore, my experience extends beyond classroom teaching. I believe in creating a caring environment where students feel encouraged to ask questions, participate in discussions, and explore the wonders of science and mathematics.

My ultimate goal as a tutor is to inspire a passion for these subjects while genuinely helping students achieve their academic goals. I am committed to providing comprehensive support, personalized guidance, and a rewarding educational experience to every student I work with.

I am confident that my dedication, expertise, and ability to inspire learning will make a significant difference in my students' educational journey. I look forward to contributing to the academic success of those I teach.

I am excited to work with students and make a positive difference through private tutoring.

Regards,
Georgio

Mohamed

5.0

(5)

Dear future baccalaureate graduate,

The physics and chemistry exam for the baccalaureate requires a solid grasp of the subject matter, effective methodology, and regular practice. I will guide you through your preparation so you can approach the exam with confidence and composure.

🎯 Why choose this support?

✅ Effective methodology: learn to analyze exercises, organize your answers and manage your time during the exam.

✅ Targeted review of the program: mastery of essential concepts in physics and chemistry.

✅ Intensive training: baccalaureate-style exercises, exam series and detailed corrections.

✅ Personalized follow-up: support adapted to your level, your difficulties and your objectives.

📚 What you get:

Clear and structured course summaries
Methodology sheets
Application exercises
Baccalaureate-style assignments under real-life conditions

My goal is to help you reinforce your knowledge, gain confidence and maximize your chances of success in the baccalaureate exam.

📩 Register now to begin your preparation.

Robert

5.0

(5)

As a Franco-Belgian teacher, I offer private lessons in physics, chemistry and biology for secondary and higher levels. I specialize in secondary level up to 5th year Belgian.

I travel, if necessary, to your home in the Brussels region as well as in Walloon and Flemish Brabant, with a minimum course duration of 2 hours. With extensive experience, I offer numerous exercises to consolidate knowledge. Distance learning is also possible via platforms such as Skype, Facebook, etc. For students in France, lessons are done exclusively remotely.

Do not hesitate to contact me to organize your lessons according to your needs and availability. I am here to help you strengthen your skills in these subjects in an effective and personalized way. Courses tailored to your needs will allow you to progress quickly.

Benson

5.0

(5)

Work with me in your IB journey. I have over 6 years of teaching experience with international students from Europe, Asia and America. I give home works and assignments on a regular basis.
Book a session with me in IB to get started. I interact with my students during lessons. After each lesson, i give students home works and assignment.

The International Baccalaureate (IB) offers several programs in Europe, including the IB Diploma Programme, the European Baccalaureate, and the IB's Primary Years Programme, Middle Years Programme, and Career-related Programme:

Poonam

5.0

(5)

Unlock your full academic potential with personalized, engaging, and effective lessons in Mathematics, Physics, Biology, Chemistry, and English. My classes are designed for students who want to not only excel in their studies but also develop a deep understanding and love for these subjects. Whether you're preparing for exams, struggling with specific concepts, or looking to advance your knowledge, this class is your gateway to success!

What You'll Get:

Tailored Learning Experience: Each lesson is customized to fit your unique learning style and academic needs. I break down complex topics into easy-to-understand concepts, ensuring you grasp the fundamentals and build a strong foundation.

Interactive and Hands-On Learning: Say goodbye to boring lectures! My classes are dynamic and interactive, filled with practical examples, problem-solving sessions, and engaging discussions that make learning enjoyable and memorable.

Comprehensive Subject Coverage: From mastering equations in Mathematics to exploring the wonders of Physics, Biology, and Chemistry, and refining your English skills, this class covers it all. You’ll gain a holistic understanding that ties together different concepts and subjects, enhancing your overall academic performance.

Continuous Support and Feedback: I’m here to support you every step of the way. You’ll receive regular feedback, personalized homework assignments, and access to additional resources to help reinforce your learning outside of class hours.

Results-Oriented Approach: My ultimate goal is your success. With a proven track record of helping students achieve higher grades and build confidence in their abilities, I’m committed to guiding you toward academic excellence.

Why This Class?

Expert Guidance: Learn from an experienced tutor who is passionate about teaching and dedicated to your success.
Engaging Content: Lessons that are not just educational, but also enjoyable and thought-provoking.
Flexible Scheduling: I understand that life can be busy, so I offer flexible scheduling options to fit your lifestyle.
Join My Class Today!

Don’t miss out on the opportunity to excel in your studies and develop a genuine love for learning. Whether you're aiming to ace your exams, overcome academic challenges, or simply explore new subjects with curiosity and enthusiasm, my class is the perfect choice for you.

Enroll now and take the first step toward a brighter academic future!

Prashil

5.0

(5)

Welcome to my Foundation Course in Science and Maths, specially designed for primary, secondary, and high school students in Amsterdam. This course aims to build a strong foundation in these critical subjects, ensuring students excel academically and develop a genuine love for learning.

My teaching approach is focused on making learning enjoyable and engaging. I incorporate interactive activities and hands-on experiments to bring Science and Maths concepts to life. By involving students in these dynamic learning experiences, I aim to transform abstract concepts into tangible understanding. Each session is thoughtfully designed to keep students interested and motivated, minimizing fatigue and maximizing retention.

I believe in simplifying complex topics, breaking them down into easy-to-understand segments. This approach helps students grasp and retain challenging concepts with ease. Techniques such as mnemonic devices, visual aids, and real-life examples are integral to my method, ensuring that formulas and concepts are not just memorized, but truly understood.

Regular assessments are conducted to track student progress and identify areas needing improvement. These tests also prepare students for their school exams, ultimately boosting their confidence. I understand the importance of keeping parents informed and involved in their child’s academic journey. That's why I provide weekly reports detailing their child’s progress, strengths, and areas for improvement. This continuous feedback loop ensures that parents are aware of their child’s development and can support their learning at home.

Encouraging words and positive feedback are integral to my teaching method. I strive to build students' self-confidence and to instill a love for learning through positive reinforcement. Setting achievable goals for each student, I celebrate their successes and motivate them to strive for excellence. This goal-setting approach not only drives academic success but also fosters a sense of accomplishment and self-worth.

As a tutor, my satisfaction comes from seeing my students excel and reach their full potential. My ultimate goal is to empower students with the knowledge and skills they need to succeed in Science and Maths. I am always available to support my students, offering additional help and resources as needed to ensure their success.

I foster an open environment where students feel comfortable asking questions, no matter how simple they may seem. This curiosity drives deeper understanding and encourages a proactive approach to learning. By incorporating games, puzzles, and interesting activities, I ensure that learning remains fun and engaging, keeping students excited about the subjects.

Join my Foundation Course in Science and Maths and watch your child develop a strong foundation, confidence, and a genuine love for these essential subjects. Let’s work together to achieve academic excellence and make learning a fun and rewarding experience. “Excel in Subjects, Soar in Confidence!”

Dr.

5.0

(5)

I offer personalized online tutoring (via teams , Zoom or Google Meet) and in-home sessions for students of all ages and levels. My lessons are designed to be interactive, creative, and tailored to each learner’s needs, ensuring active engagement and lasting understanding.

With a Ph.D. in Science and 10+ years of teaching experience, I provide flexible session lengths (1-2 hours) and adapt my methods—whether through discussions, multimedia, or hands-on examples—to make complex topics accessible and exciting. Let’s make learning both effective and enjoyable!

Course Subject:
Biology: Biotechnology, Biochemistry, Immunology, Cell and Molecular Biology, Molecular Genetics, Anatomy and Physiology of animals and plants

Chemistry—comprehensive coverage of all five core disciplines to ensure a holistic understanding of the molecular world.

Organic Chemistry: Reaction mechanisms, stereochemistry, synthesis planning, and nomenclature.

Inorganic Chemistry: Coordination chemistry, periodicity, molecular symmetry, and bio-inorganic systems.

Physical Chemistry: Thermodynamics, quantum chemistry, kinetics, and electrochemistry.

Analytical Chemistry: Spectroscopy (NMR, IR, UV-Vis), chromatography, method validation, and data interpretation.

Biochemistry: Enzyme kinetics, metabolic pathways, protein structure, and bioenergetics.

Course Level: Tailored for High School (IB/AP/A-Levels), University/College (Undergraduate & Graduate), and Adult Learners seeking to strengthen fundamentals or prepare for competitive exams.

Location of the Lessons: Live, interactive, and high-quality sessions delivered online—learn from home in the Netherlands or anywhere worldwide, Face to face- at your home or at my place.

Iskander

5.0

(5)

I hold a Doctorate in Pharmacy and 2 Masters degrees from the University of Paris V René-Descartes.
Since the beginning of my higher education, and since I established myself as a freelancer after 10 years of managerial career in the pharmaceutical industry, I have been used to regularly giving private lessons to pupils and students of all levels, Primary, Secondary and Higher, supporting them until they pass their exams.
The main disciplines in which I support students are essentially scientific.
The perspectives provided are transdisciplinary.

Elvis

5.0

(5)

Struggling with equations, chemical reactions, or physics problems that just don't seem to click? I help students go from confused and frustrated to confident and capable — one concept at a time.

I offer tutoring in Mathematics, Chemistry, and Physics for students from middle school through high school (and university-level for select topics). My approach focuses on building real understanding rather than memorization, so students can tackle new problems on their own, not just the ones we've practiced together.

What I offer:

Personalized lessons tailored to your learning style and pace
Clear explanations that break complex topics into manageable steps
Exam and test preparation (finals, standardized tests, entrance exams)
Homework help and concept reinforcement
Practice problems with detailed feedback
Patient, judgment-free environment — no question is too basic

Why work with me:
I don't just teach formulas — I teach how to think through problems, so students build genuine confidence, not dependence on a tutor. Many students come to me feeling like they're "bad at math" or "not a science person," and leave realizing they just needed the right explanation.

Available for online and in-person sessions. Flexible scheduling to fit your routine. First session includes a quick assessment so we can build a plan targeted to your specific gaps and goals.

📩 Message me to discuss your (or your child's) needs — let's turn these subjects from a source of stress into a strength.