C7: Rates Of Reaction And Energy Changes

Question 1

What is the equation for rate of reaction?

Answer 1

Rate of reaction = amount of reactant used or product formed / time (s)

Question 2

What units could be used for rate of reaction?

Answer 2

g/s
cm3/s
mol/s

Question 3

How can you measure the rate of reaction when a gas is given off?

Answer 3

• measure time and collect gas in an upside down measuring cylinder in a trough of water or in a gas syringe to measure the volume of gas produced
• measure time and the change in mass

Question 4

How can you measure the rate of reaction when a precipitate is formed?

Answer 4

• put a black cross below a beaker containing one reactant
• time how long it takes for cross to disappear after the second reactant is added

Question 5

What does activation energy mean?

Answer 5

The minimum amount of energy required for a reaction to occur between two reacting particles

Question 6

What must happen for a reaction to occur?

Answer 6

Particles must collide at the correct orientation with sufficient energy to react

Question 7

In terms of particles, what 2 things could happen when the rate of reaction increases?

Answer 7

• more frequent collisions
• energy of collisions increases

Question 8

How can the rate of reaction be increased?

Answer 8

• increase the temperature
• increase concentration
• increase surface area to volume ratio
• add a catalyst

Question 9

How does surface area affect the rate of reaction?

Answer 9

Increasing surface area of reactants increases the rate of reaction, this is because a greater surface area means there are more exposed particles so more frequent successful collisions

Question 10

How does catalyst affect the rate of reaction?

Answer 10

• increases rate of reaction
• because it provides an alternate reaction pathway with a lower activation energy
• more particles will have sufficient energy to overcome the activation energy and react
• so more successful collisions occur in the same time

Question 11

What is a catalyst?

Answer 11

A substance which speeds up the rate of reaction without being chemically changed at the end

Question 12

How does a catalyst speed up the rate of reaction?

Answer 12

It provides an alternate reaction pathway with a lower activation energy

Question 13

What are enzymes?

Answer 13

Act as a biological catalyst that increases the rate of reactions in living cells

Question 14

Which enzyme is used to produce ethanol from glucose?

Answer 14

Yeast

Question 15

What are 2 types of exothermic reactions?

Answer 15

• combustion
• neutralisation

Question 16

What are 2 types of endothermic reactions?

Answer 16

• thermal decomposition
• photosynthesis