Reaction rates and equilibrium

Question 1

what two conditions must occur for an effective collision.

Answer 1

1. particles must collide with the correct orientation.
2. The particles must have sufficient energy to overcome the activation of the reaction.

Question 2

What four factors change the rate of chemical reaction.

Answer 2

1. Concentration (pressure in gasses)
2. Temperature
3. Use of a catalyst
4. Surface area of solid reactants.

Question 3

Why does concentration or pressure of gas affect the rate of reaction?

Answer 3

When the concentration or pressure for gasses increases, the number of particles increases for the same volume, the particles are closer together and collide more frequently, resulting in more succesful collisions per unit time, increasing the rate of reaction.

Question 4

What can the rate of reaction be defined as?

Answer 4

The change in concentration of a reactant or product over time.

Question 5

what graph is rate of reaction the gradient of?

Answer 5

Concentration time graph.

Question 6

What does a catalyst do?

Answer 6

Increases the rate of a chemical reaction without being used up in the overall equation. The catalyst increases the rate of reaction by providing an alternative pathway with a lower activation energy.

Question 7

What is the difference between homogeneous and heterogeneous catalysts?

Answer 7

Homogeneous catalysts are the same physical state as the reactants. A heterogeneous catalyst has a different physical state as the reactants.

Question 8

How does a homogeneous catalyst work?

Answer 8

Th catalysts reacts with the reactants to form an intermediate compound, which then breaks down to reproduce the catalyst and produce the products.

Question 9

How does a heterogeneous catalyst work?

Answer 9

Heterogeneous catalysts are usually solids, their reactant a (usually gas or aqueous solution) are absorbed into the surface of the catalyst, react to produce the product and catalyst then the product deabsorbs out of the catalyst.

Question 10

What is the economic and sustainable impacts of catalysts?

Answer 10

Catalysts reduce the activation energy needed for a reaction, this inturn requires less energy for the react to occur, leading to less electricity use.
- leading to less fossil fuels being burnt to produce the electricity.
- Leading to larger profits as less is spent on electricity.

Question 11

Why might a catalyst not be beneficial for the enviroment?

Answer 11

The catalyst could be toxic and prove worse for the enviroment.

Question 12

What two methods areused to measure rate of reaction?

Answer 12

1. Loss of mass by mass balance.
2. Volume of gass produced using gass collection.
   -Both should be measured over a period of time

Question 13

Why can mass loss and volume gain be used to measure rate of reaction?

Answer 13

Both volume of gass produced and mass lost are proportional to rate of reaction.

Question 14

What does the Boltzman distribution show?

Answer 14

The distribution of molecular energies in gases.

Question 15

What are the features of the Boltzman distribution?

Answer 15

1. No molecules have zero energy (Curve starts at the origin)
2. The area under the graph is equal to the total number of molecules.
3. There is no maxiumum energy for a molecule, the curve never touches the x axis after the origin / at high energy.

Question 16

What does the temperature do to the boltzman distribution?

Answer 16

Lowers and shifts the peak to the right.

Question 17

What does increasing the tempertaure do to the rate of reaction?

Answer 17

Leads to a higher rate of reaction.
More molecules have a greater or equal amount of energy to the activation energy, leading to more succesful collisions and a higher rate of reaction

Question 18

What does adding a catalyst do to the rate of reaction?

Answer 18

Lowers the activation energy so a larger proportion of molecules can succesfuly react leading to a high rate of reaction.

Question 19

Define dynamic equilibrium

Answer 19

The rate of forward raction is equal to that of the rate of reverse reaction. The concentration of the reactants and products saty the same.

Question 20

what does Le chatelier’s principle state?

Answer 20

when a system in equilibrium is subject to external change, the system adjusts to minimise said change.

Question 21

what happends to the equilibrium constant if more products or reactants are formed?

Answer 21

1. If more products are formed the equilibrium constant shifts to the right (products).
2. If more reactants are formed the equilibrium constant shifts to the left (reactants).

Question 22

For the equation
2CrO4 2- + 2H+ -> Cr2O7 2- + H2O
(yellow) (orange)
what happens if acid (H+) is added?

Answer 22

When acid is added the H+ ion concentration increases, the forward reactions increases to produce more product (Cr2O7 2- and H2O) to minimise the change the addition of H+ ions. The position of equilibrium therefore shifts to the right. A stronger orange colour is seen.

Question 23

For the equation
2CrO4 2- + 2H+ -> Cr2O7 2- + H2O
(Yellow) (Orange)
what happens if base (OH-) is added?

Answer 23

When (OH-) ions are added the concentration of H+ ions decreases, the rate of the forward reaction decreases to increase the concentration of H+ ions to minimise the change. A new position of equilibrium is established, shifted to the left. Yellow colour should be seen more.

Question 24

What happens to the position of equilibrium if an increase in temperature occurs and why?

Answer 24

The position of equilibrium shifts towards the endothermic side, to take in heat energy, minimising the change (increase in temp).

Question 25

What happens to the position of equilibrium if a decrease in temperature occurs and why?

Answer 25

The position of equilibrium shifts to the exothermic side, in an attempt to produce more heat energy minimising the change to the system (decrease in temp).

Question 26

What happens to the position of equilibrium if a catalyst is added and why?

Answer 26

Position of equilibrium does not change.
Because the rate of forward and backward reactions are the same.
However the rate of reaction is sped up.

Question 27

Why is dynamic equilibrium used in industry and to waht extent?

Answer 27

Changing the temperature and pressure, shifts the position of equilibrium towards the right side (to produce more product). However high pressures and temperatures are deangerous and expensive, so this should only be done to an extent.

Question 28

Where is the position of equilibrium if Kc > 1

Answer 28

Towards the right side (products)

Question 29

Where is the position of equilibrium if Kc < 1

Answer 29

Towards the left side (reactants).