Kinetics And Equilibria

Question 0

The rate equation links ……………. to ……………..

Answer 0

Reaction rate

Reactant concentrations

Question 1

What is the reaction rate

Answer 1

The change in the amount of reactants or products per unit time. If the reactants are in solution, the rate will change in concentration per second

Question 2

What is the initial rate of a reaction

Answer 2

The rate right at the start of the reaction, can find this from a conc-time graph by calculating the gradient of the tangent at time = 0

Question 3

Explain how to use the initial rates method

Answer 3

Repeat experiment several times using different initial concs of reactants, should only change one of the concs at a time keeping the rest constant

Calculate the initial rate for each experiment

See how the initial concs affect the initial rates and figure out the order for each reactant

Question 4

The rate determining step is the …………. step in a multi step reaction

Answer 4

Slowest

Question 5

Important things to remember about the rate determining steps and mechanisms

Answer 5

Rate determining step doesn’t have to be the first step in a mechanism

The reaction mechanism can’t usually be predicted from just the chemical equation

Question 6

The order of a reaction with respect to a reactant shows….

Answer 6

The number of molecules of that reactant that are involved in the rate determining step

Question 7

The rate determining step can help you to work out….

Answer 7

The reaction mechanism

Question 8

What is dynamic equilibrium

Answer 8

Happens in closed system. Forward and backward reactions are proceeding at equal rates. The conc/moles of reactants and products remain constant

Question 9

Equilibria can be set up in physical systems. Example

Answer 9

When liquid bromine is shaken in a closed flask, some of it changes to orange bromine gas. After a while, equilibrium is reached, bromine liquid is still changing to bromine gas and bromine gas is still changing to bromine liquid, but changing at same rate

Question 10

Equilibria can be set up in chemical systems. Example

Answer 10

If hydrogen gas and iodine gas are mixed together in a closed flask, hydrogen iodide is formed. The amounts of hydrogen iodide, hydrogen and iodine will never change no matter how long they are left for

Question 11

Catalysts have no effect on the position of equilibrium or on the value of Kc. Can’t increase yield, but do mean what?

Answer 11

equilibrium is approached faster

Question 12

What 3 things affect the position of equilibrium

Answer 12

Temp

Conc

Pressure

Question 13

What is Le Chateliers principle

Answer 13

If you change the conc, pressure or temp of an equilibrium reaction, the equilibrium will move to help counteract the change

Question 14

How does temp alter Kc

Answer 14

Increase in temp means eqm shifts in endothermic direction to absorb heat. Decreasing the temp means eqm shifts in exothermic direction to replace heat. If a change means more product is formed Kc will rise. If it means less product is formed then Kc will decrease

Question 15

How does conc alter Kc

Answer 15

The value of the eqm constant is fixed at given temp. So if the conc of one thing in the eqm mixture changes then the concs of the others must change to keep the value of Kc the same

Question 16

Do catalysts have an effect on the value of Kc

Answer 16

No

Question 17

Is Kc effected by conc

Answer 17

No

Question 18

Is Kc effected by temp

Answer 18

Yes

Question 19

How does an increase in temp effect the rate constant

Answer 19

If the temp increases the rate constant also increased due to increasing number of collisions between reactant molecules

Question 20

How does volume effect Kc

Answer 20

It changes the pressure. Only effects Kc if there are different number of moles on either side of equation