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Class 10·Science
Class 10 · Science

Chemical Reactions and Equations

Chemical reactions are the foundation of chemistry.

Feynman Lens

Start with the simplest version: this lesson is about Chemical Reactions and Equations. If you can explain the core idea to a friend using everyday language, examples, and one clear reason why it matters, you have moved from memorising to understanding.

Chemical reactions are the foundation of chemistry. When substances interact and transform into completely new materials with different properties, a chemical reaction occurs. In our daily lives, burning fuel, rusting iron, digesting food, and even breathing all involve chemical reactions. This chapter teaches us how to recognize when a chemical reaction happens and how to represent these changes using chemical equations—a universal language for understanding what happens at the molecular level.

What Happens During a Chemical Reaction?

Imagine you're baking a cake. You mix flour, eggs, milk, and sugar—each ingredient is distinct. But once you heat the mixture, something magical occurs: these separate ingredients chemically transform into something entirely new. The same happens when magnesium metal burns in oxygen—the shiny metal and colorless gas combine to form white powder (magnesium oxide).

A chemical reaction occurs when:

The key insight: substances are not just rearranging themselves. Their very identity changes at the atomic level. The bonds holding atoms together break, and new bonds form, creating entirely different substances.

How Do We Write Chemical Equations?

Think of a word equation as a recipe: "Magnesium + Oxygen → Magnesium oxide." It tells us what we start with (reactants) and what we end with (products). But scientists use chemical symbols to be more precise. Instead of words, we write: Mg + O₂ → MgO

However, this equation has a problem. On the left side, we have 2 oxygen atoms (in O₂), but on the right side, we only have 1 oxygen atom (in MgO). Atoms cannot disappear! This violates the Law of Conservation of Mass. So we must balance the equation: 2Mg + O₂ → 2MgO

Now both sides have the same number of each type of atom, just like a balanced scale.

Key Concepts

Reactants: The starting substances that undergo change (written on the left side of the arrow).

Products: The new substances created by the reaction (written on the right side).

Coefficients: The numbers placed before chemical formulas to balance equations. They tell us how many molecules or atoms participate in the reaction.

Skeletal equation: An unbalanced chemical equation that shows what reacts but not the correct quantities.

Balanced equation: A properly balanced equation where the number of atoms of each element is the same on both sides.

When balancing, always remember: you can only change coefficients, never the subscripts in chemical formulas.

Real-World Applications

Chemical equations help us understand:

Acids, Bases and Salts - many important reactions involve acids and bases

Carbon and its Compounds - combustion and carbon reactions

Socratic Questions

  1. Why can't we simply create new atoms or destroy existing atoms when a chemical reaction occurs, and what does this tell us about how matter is conserved?
  1. If you balance an equation by changing subscripts instead of coefficients, you would create different substances—why is this fundamentally different from what actually happens in a reaction?
  1. When you see a product that looks completely different from its reactants, what is actually happening at the atomic level that causes this dramatic change?
  1. How would you explain to someone why writing "Mg + O₂ → MgO" (unbalanced) is scientifically incorrect, even though it shows the correct reactants and products?
  1. Can you think of a chemical reaction you've observed in everyday life and predict what new substance must have formed based on the signs that a reaction occurred?
🃏 Flashcards — Quick Recall
Term / Concept
What is Chemical Reactions and Equations?
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Chemical Reactions and Equations is the central idea of this lesson. Use the chapter examples to explain what it means and why it matters.
Term / Concept
What is The state changes?
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(solid becomes gas, or liquid changes color)
Term / Concept
What is The color transforms?
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(iron rusts from silver to brown)
Term / Concept
What is Gas is released?
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(fizzing when vinegar meets baking soda)
Term / Concept
What is Temperature changes?
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(reaction feels hot or cold)
Term / Concept
What is An irreversible change happens?
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(paper burning cannot be undone)
Term / Concept
What is Reactants?
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The starting substances that undergo change (written on the left side of the arrow).
Term / Concept
What is Products?
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The new substances created by the reaction (written on the right side).
Term / Concept
What is Coefficients?
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The numbers placed before chemical formulas to balance equations. They tell us how many molecules or atoms participate in the reaction.
Term / Concept
What is Skeletal equation?
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An unbalanced chemical equation that shows what reacts but not the correct quantities.
Term / Concept
What is Balanced equation?
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A properly balanced equation where the number of atoms of each element is the same on both sides.
Term / Concept
What is the core idea of What Happens During a Chemical Reaction??
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Imagine you're baking a cake. You mix flour, eggs, milk, and sugar—each ingredient is distinct.
Term / Concept
What is the core idea of How Do We Write Chemical Equations??
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Think of a word equation as a recipe: "Magnesium + Oxygen → Magnesium oxide." It tells us what we start with (reactants) and what we end with (products). But scientists use chemical symbols to be more precise.
Term / Concept
What is the core idea of Key Concepts?
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Reactants: The starting substances that undergo change (written on the left side of the arrow). Products: The new substances created by the reaction (written on the right side).
Term / Concept
What is the core idea of Real-World Applications?
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Chemical equations help us understand: - How plants convert sunlight into food through photosynthesis - How cars burn fuel and release exhaust - How our bodies digest food to produce energy - How batteries work through…
Term / Concept
What is The state changes (solid becomes gas, or?
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The state changes (solid becomes gas, or liquid changes color)
Term / Concept
What is The color transforms (iron rusts from silver?
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The color transforms (iron rusts from silver to brown)
Term / Concept
What is Gas is released (fizzing when vinegar meets?
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Gas is released (fizzing when vinegar meets baking soda)
Term / Concept
What is Temperature changes (reaction feels hot or cold)?
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Temperature changes (reaction feels hot or cold)
Term / Concept
What is An irreversible change happens (paper burning cannot?
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An irreversible change happens (paper burning cannot be undone)
Term / Concept
What is How plants convert sunlight into food through?
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How plants convert sunlight into food through photosynthesis
Term / Concept
What is How cars burn fuel and release exhaust?
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How cars burn fuel and release exhaust
Term / Concept
What is How our bodies digest food to produce?
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How our bodies digest food to produce energy
Term / Concept
What is How batteries work through chemical reactions?
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How batteries work through chemical reactions
Term / Concept
Why What Happens During a Chemical Reaction? matters?
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What Happens During a Chemical Reaction? matters because it connects the chapter idea to a reason, pattern, or method you can apply in problems.
Term / Concept
Why How Do We Write Chemical Equations? matters?
tap to flip
How Do We Write Chemical Equations? matters because it connects the chapter idea to a reason, pattern, or method you can apply in problems.
Term / Concept
Why Key Concepts matters?
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Key Concepts matters because it connects the chapter idea to a reason, pattern, or method you can apply in problems.
Term / Concept
Why Real-World Applications matters?
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Real-World Applications matters because it connects the chapter idea to a reason, pattern, or method you can apply in problems.
Term / Concept
What is a good example of What Happens During a Chemical Reaction??
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A good example of What Happens During a Chemical Reaction? should show the idea in action rather than only repeat its definition.
Term / Concept
What is a good example of How Do We Write Chemical Equations??
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A good example of How Do We Write Chemical Equations? should show the idea in action rather than only repeat its definition.
Term / Concept
What is a good example of Key Concepts?
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A good example of Key Concepts should show the idea in action rather than only repeat its definition.
Term / Concept
What is a good example of Real-World Applications?
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A good example of Real-World Applications should show the idea in action rather than only repeat its definition.
Term / Concept
What is a common trap in What Happens During a Chemical Reaction??
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A common trap in What Happens During a Chemical Reaction? is memorising the statement without checking when and why it applies.
Term / Concept
What is a common trap in How Do We Write Chemical Equations??
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A common trap in How Do We Write Chemical Equations? is memorising the statement without checking when and why it applies.
Term / Concept
What is a common trap in Key Concepts?
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A common trap in Key Concepts is memorising the statement without checking when and why it applies.
Term / Concept
What is a common trap in Real-World Applications?
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A common trap in Real-World Applications is memorising the statement without checking when and why it applies.
Term / Concept
How should you think about How to explain What Happens During a Chemical Reaction??
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To explain What Happens During a Chemical Reaction?, begin with the simplest case, name the quantities involved, and then add complexity step by step.
Term / Concept
How should you think about How to explain How Do We Write Chemical Equations??
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To explain How Do We Write Chemical Equations?, begin with the simplest case, name the quantities involved, and then add complexity step by step.
Term / Concept
How should you think about How to explain Key Concepts?
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To explain Key Concepts, begin with the simplest case, name the quantities involved, and then add complexity step by step.
Term / Concept
How should you think about How to explain Real-World Applications?
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To explain Real-World Applications, begin with the simplest case, name the quantities involved, and then add complexity step by step.
40 cards — click any card to flip
📝 Quick Quiz — Test Yourself
Why can't we simply create new atoms or destroy existing atoms when a chemical reaction occurs, and what does this tell us about how matter is conserved?
  • A Memorize the exact line without checking the reasoning.
  • B Use the chapter's evidence and explain the reasoning step by step.
  • C Ignore the examples and rely only on a keyword.
  • D Treat the idea as unrelated to the rest of the lesson.
If you balance an equation by changing subscripts instead of coefficients, you would create different substances—why is this fundamentally different from what actually happens in a reaction?
  • A Memorize the exact line without checking the reasoning.
  • B Use the chapter's evidence and explain the reasoning step by step.
  • C Ignore the examples and rely only on a keyword.
  • D Treat the idea as unrelated to the rest of the lesson.
When you see a product that looks completely different from its reactants, what is actually happening at the atomic level that causes this dramatic change?
  • A Memorize the exact line without checking the reasoning.
  • B Use the chapter's evidence and explain the reasoning step by step.
  • C Ignore the examples and rely only on a keyword.
  • D Treat the idea as unrelated to the rest of the lesson.
How would you explain to someone why writing "Mg + O₂ → MgO" (unbalanced) is scientifically incorrect, even though it shows the correct reactants and products?
  • A Memorize the exact line without checking the reasoning.
  • B Use the chapter's evidence and explain the reasoning step by step.
  • C Ignore the examples and rely only on a keyword.
  • D Treat the idea as unrelated to the rest of the lesson.
Can you think of a chemical reaction you've observed in everyday life and predict what new substance must have formed based on the signs that a reaction occurred?
  • A Memorize the exact line without checking the reasoning.
  • B Use the chapter's evidence and explain the reasoning step by step.
  • C Ignore the examples and rely only on a keyword.
  • D Treat the idea as unrelated to the rest of the lesson.
Which approach best shows that you understand Chemical Reactions and Equations?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand The state changes?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand The color transforms?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Gas is released?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Temperature changes?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand An irreversible change happens?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Reactants?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Products?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Coefficients?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Skeletal equation?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Balanced equation?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand What Happens During a Chemical Reaction??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand How Do We Write Chemical Equations??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Key Concepts?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Real-World Applications?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand The state changes (solid becomes gas, or?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand The color transforms (iron rusts from silver?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Gas is released (fizzing when vinegar meets?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Temperature changes (reaction feels hot or cold)?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand An irreversible change happens (paper burning cannot?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand How plants convert sunlight into food through?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand How cars burn fuel and release exhaust?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand How our bodies digest food to produce?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand How batteries work through chemical reactions?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Why What Happens During a Chemical Reaction? matters?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Why How Do We Write Chemical Equations? matters?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Why Key Concepts matters?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Why Real-World Applications matters?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Example of What Happens During a Chemical Reaction??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Example of How Do We Write Chemical Equations??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Example of Key Concepts?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Example of Real-World Applications?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Common trap in What Happens During a Chemical Reaction??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Common trap in How Do We Write Chemical Equations??
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
Which approach best shows that you understand Common trap in Key Concepts?
  • A Repeat its name from memory.
  • B Explain it using a simple example and the reason it works.
  • C Skip the conditions where it applies.
  • D Use it only when the textbook wording is identical.
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