1. Definition
Rate of Reaction: The change in quantity of reactants/products per unit time.
Measured by:
Volume of gas produced per second (cm³/s).
Mass of substance formed/lost per second (g/s).
🧪 2. Factors Affecting the Rate of Reaction
a) Concentration
Higher concentration → more particles → more frequent collisions → faster reaction.
b) Temperature
Higher temperature → particles move faster → more collisions with sufficient energy.
c) Size of Reactants (Surface Area)
Smaller particles (powdered) → larger surface area → more frequent collisions.
d) Catalyst
Speeds up reaction without being used up.
Lowers activation energy required.
⚛️ 3. Collision Theory
Reaction occurs when particles collide with sufficient energy and correct orientation.
Effective collisions lead to product formation.
📈 4. Measuring Rate of Reaction (Experiments)
Marble chips + HCl → measure volume of CO₂.
Thiosulphate + HCl → observe cloudiness (formation of sulfur).
Magnesium + acid → measure hydrogen gas released.
📉 5. Rate Graph
Steep slope = fast reaction.
Flat line = reaction has stopped (no more reactants).
Compare slopes to determine reaction speed.
📎 6. Importance in Daily Life / Industry
Fast reactions: fireworks, digestion.
Controlled reactions: medicine production, food preservation.
Use of catalysts in:
Haber Process (ammonia) – iron catalyst.
Hydrogenation of oil – nickel catalyst.
📈 1. Volume of Gas vs Time
- The graph starts steep (fast reaction at the beginning).
- It gradually flattens as the reaction slows and finally stops.
- Indicates how much gas is produced over time.
📉 2. Mass vs Time
- Shows the decrease in mass as gas escapes from the reaction.
- Sharp drop at the start, then levels off.
- Common in reactions where gas is a product (e.g. acid + carbonate).
📊 3. Rate of Reaction vs Time
- Highest rate at the beginning due to abundant reactants.
- Rate drops as reactants are used up.
- Ends at zero when the reaction stops.
| Factor | Effect on Collision Theory | Explanation |
|---|---|---|
| Size of Reactants (Surface Area) | Increased surface area increases frequency of collisions | Smaller particles expose more surface for collisions, leading to more effective collisions. |
| Concentration | Higher concentration leads to more collisions | More particles per unit volume result in a higher frequency of collision. |
| Catalyst | Provides an alternative pathway, reducing activation energy | Catalysts speed up the reaction rate by reducing the energy required for effective collisions to occur. |