CHAPTER 10: Reaction Rates & Equilibrium

Question 1

What is RATE OF REACTION?

Answer 1

a measure of how fast a reactant is used up or how fast a product is formed.

Question 2

What is the general pattern of rate of reaction ?

Answer 2

• Rate is fastest at start as each reactant is at its highest concentration.
• Slows down as reaction proceeds because reactants being used up and conc decreases.
• when one of the reactant has been completely used up the rate of reaction is 0 as reaction stops.

Question 3

What 4 things affect rate of reaction?

Answer 3

1) Catalyst
2) Surface area of reactants
3) temperature
4) concentration or pressure for gases

Question 4

Describe the collision theory.

Answer 4

two reacting particles must collide with correct orientation and sufficient energy to overcome activation energy for a reaction to occur.

Question 5

How does increasing CONCENTRATION affect the ROR?

Answer 5

increasing conc increases the number of particles in the same volume so particles are closer together and colliding more frequently so more successful collisions in a given time.

Question 6

How does increasing PRESSURE affect the ROR?

Answer 6

Increasing pressure means more particles in a smaller volume so collisions are more frequents so more successive collisions in a given time.

Question 7

What are 2 ways of measuring the progress of a reaction to measure the rate?

Answer 7

1) monitor the removal of reactant

2) or formation of a product

Question 8

When do you know a reaction is complete when monitoring a reaction that produces gas by weighing it?

Answer 8

When no more gas is produced so there is no change in scale reading.

Question 9

What are catalysts?

Answer 9

a substance that changes the rate of reaction without undergoing any permanent change by providing a route with a lower activation energy.

Question 10

What are HOMOGENOUS catalysts?

Answer 10

catalysts that has same physical state as reactants.
they work by reacting with reactants to form intermediate that then breaks down to give the product and regenerates the catalyst.

Question 11

What are HETEROGENOUS catalysts?

Answer 11

catalysts with different physical state as reactants.
tend to provide a surface for the reaction to take place.
reactant molecules are ABSORBED onto the surface and products leave through DESORPTION.

Question 12

How are catalysts sustainable and economical?

Answer 12

• less need for energy so reduces temp - less fossil fuels and so less emissions of carbon dioxide.
• cuts cost of energy so more profit.

Question 13

What is on the axes of a boltzmann distribution?

Answer 13

y axis - number of molecules with a given energy.

x axis - energy

Question 14

What are the 3 main features about a boltzmann distribution?

Answer 14

1) starts at zero because no molecules = no energy.
2) Area under curve equals the total number of molecules.
3) no maximum energy for a molecule so curve never meets x axis.

Question 15

What happens to the boltzmann distribution when the temperature is increased?

Answer 15

• area stays the same
• more molecules with higher energy so height decreases and peak shifts slightly to right.
• more molecules with equal to or greater than activation energy

Question 16

What happens to boltzmann distribution when catalysts are added?

Answer 16

The activation energy shifts to left so more molecules have energy equal to or greater than the lowered activation energy.

Question 17

What are the 2 features of an equilibrium system?

Answer 17

1) rate of forward reaction is equal to the rate of reverse reaction.
2) concentrations of reactant and products do not change.

Question 18

Why does a reaction need to be in a closed system to remain in equilibrium?

Answer 18

So that temperature, concentrations of reactants and products are unaffected by outside influences.

Question 19

What does le Chatelier’s principle state?

Answer 19

When a system in equilibrium is subjected to external change, the system readjusts itself to minimise the effect of that change.

Question 20

Which way does the equilibrium move when concentration changes?

Answer 20

Moves towards the higher concentration.

more products, shifted to right.

Question 21

Which way does equilibrium move when temperature changes?

Answer 21

INCREASE in temp shifts equilibrium towards endothermic reaction.
DECREASE in temp shifts equilibrium towards exothermic reaction.

Question 22

How does pressure affect equilibrium position?

Answer 22

Shifts it to the side with fewer particles (mols)

Question 23

What affect does catalysts have on the equilibrium position.

Answer 23

NONE.

it just speeds up the rate at which the equilibrium can be reached.

Question 24

How do you calculate equilibrium constant (Kc)?

Answer 24

[products] ÷ [reactant]

with mol no. as power.

Question 25

What does the equilibrium constant tell us?

Answer 25

• position of equilibrium
• whether there are more reactants or products in an equilibrium system.
  Kc > 1 = more reactants as equilibrium towards right
  Kc