Day 5: Collision Theory & Reaction Rates | Secondary Stage Science | Apex Institute of Maths and Sciences

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Day 5: Collision Theory & Reaction Rates ⚡

Secondary Stage Science | APEX EDUTECH SOLUTIONS

🎯 1. Concept: Collision Theory

For a chemical reaction to occur, reactant particles must collide. However, not all collisions result in a reaction. To be “effective,” a collision requires:

  • Sufficient Energy: Particles must collide with energy equal to or greater than the Activation Energy ($E_a$).
  • Correct Orientation: Particles must hit each other in the right direction to break and form bonds.

💡 2. Factors Increasing Reaction Rate

The rate of reaction can be increased by increasing the frequency or energy of collisions:

1. Temperature: Increases kinetic energy of particles.
2. Concentration: Increases the number of particles in a given volume.
3. Surface Area: More area for collisions to occur (powder vs. solid chunk).
4. Catalyst: Lowers the Activation Energy ($E_a$) without being consumed.
[Image of reaction coordinate diagram with and without catalyst]

🌍 3. Science in Our Daily Life

Scenario: Why do we keep food in a refrigerator? At lower temperatures, the kinetic energy of bacteria and enzyme particles decreases. This reduces the frequency and force of collisions, significantly slowing down the chemical reactions that lead to food spoilage.

📝 4. Home Research Task

Perform the Surface Area Experiment. Take two identical effervescent (antacid) tablets. Drop one whole into a glass of water and crush the second into powder before dropping it into another glass. Measure which one finishes reacting (fizzing) first. Explain the result using Collision Theory.

✅ 5. Day 5 Advanced Assessment

All answers are derived from the collision mechanics provided above.

Easy
1. The minimum energy required for a collision to result in a reaction is called:
Solution: Activation energy is the “energy barrier” particles must overcome (Part 1).
Easy
2. Which factor increases the surface area of a reactant?
Solution: Powdering increases the available area for collisions (Part 2 & 4).
Easy
3. What is a substance that speeds up a reaction without being used up?
Solution: A catalyst provides an alternative path with lower $E_a$ (Part 2).
Easy
4. Increasing the concentration of reactants increases the rate because:
Solution: More particles in a space lead to more frequent hits (Part 2).
Medium
5. Why does high temperature speed up a reaction?
Solution: Particles move faster and hit harder at higher temperatures (Part 2).
Medium
6. An “effective collision” must have both sufficient energy and:
Solution: Particles must hit at the right angle to react (Part 1).
Medium
7. How does a catalyst change the activation energy?
Solution: It makes the “hill” smaller so more particles can get over it (Part 2).
Medium
8. Food spoils faster at room temperature than in a fridge because:
Solution: Heat accelerates the chemical reactions of decay (Part 3).
Hard
9. Assertion: Not all collisions lead to a chemical reaction.
Reason: Collision theory requires specific energy and orientation for success.
Solution: Most collisions are “elastic” and don’t result in bonds breaking (Part 1).
Hard
10. If you double the temperature, the rate increases mainly because:
Solution: Temperature doesn’t change $E_a$, it just gives more particles the energy to reach it (Part 2).

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