Chemical Reactions part 1

Question 1

Define chemical change

Answer 1

Reactants -> Products
Products have different properties to the reactants
Most are irreversible
Eg. Combustion reaction

Question 2

Define physical change

Answer 2

The substance itself does not change, it just takes on a different form
Eg. Phase/State changes

Question 3

Define rate of reaction

Answer 3

The change in concentration per unit of time of either the product or the reactant

Question 4

Define collision theory

Answer 4

A reaction will only occur when an effective collision takes place. The more effective collisions take place per unit time, the faster the rate of reaction.

Question 5

What are the 5 factors that affect the rate of reaction? Explain each.

Answer 5

1. Increase concentration - Liquids
   Increase number of particles, therefore increase number of collisions
2. Increase temperature
   Particles have more energy -> Move faster -> More frequent collisions -> collisions have more energy
3. Decrease volume / Increase pressure - Gases
   Particles are closer together, more collisions
4. Catalyst
   Lowers activation energy
5. Increase surface area - solids
   More area for particles to collide with, therefore more collisions

Question 6

Explain temperature as a factor of affecting the rate of reaction.

Answer 6

As temperature increases, particles gain kinetic energy and move faster; which results in:
More collisions per second
More of the colliding particles have sufficient energy to react
Temp up, Rate of reaction up

Question 7

Explain concentration as a factor of affecting the rate of reaction.

Answer 7

The higher the concentration, the more particles per unit volume
Results in more effective collisions per unit time and a faster reaction rate.

Question 8

Explain catalyst as a factor of affecting the rate of reaction.

Answer 8

Def: A catalyst increases the rate of reaction and is unchanged at the end of the reaction
Mechanism: The catalyst decreases the activation energy of the reaction
Result: More collisions with be effective as more molecules collide with equal to or greater than the activation energy
More effective collisions lead to a faster reaction rate.

Question 9

Explain surface area as a factor of affecting the rate of reaction.

Answer 9

Smaller the particle size -> greater surface area eg. powder vs chunks
Greater the surface area -> More surface exposed for the reaction to take place
Results in more effective collisions per unit time

Question 10

Explain pressure as a factor of affecting the rate of reaction.

Answer 10

Increase pressure by reducing volume -> reduce space in which the gas particles can move
Results in more effective collisions per unit time and a faster reaction rate

Question 11

What are the 2 methods of measuring the rate of reaction?

Answer 11

1. Measure the volume of gas given off every minute
2. Measure the decrease in mass of the reactant as the gas escapes