Equilibrium

Question 1

Describe the forward and backward reaction in a reversible reaction

Answer 1

-Forward reaction: initially reactants are used up quickly but then slow as their concentration drops
-Backward reaction: initially reactants are reformed slowly but then speed up as the concentration of products increases.

Question 2

What is dynamic equilibrium?

Answer 2

point at which the rate of the forward reaction equals the rate of the backward reaction. The concentration of each substance remains constant. This only occurs in a closed system.

Question 3

How can you calculate Kc?

Answer 3

the concentration of the products/ the concentration of the reactants
-the molar values in front of each species are the powers in the Kc expression

Question 4

concentration units?

Answer 4

moldm-3

Question 5

What is a homogeneous reaction?

Answer 5

all reactants and products are in the same state so all reactants and products are included in the final Kc expression.

Question 6

What is a heterogenous reaction?

Answer 6

all reactants and products are in different states so we don’t include solids and pure liquids in the final Kc expression. This is due to their concentrations remaining constant.

Question 7

What does the ICE acronym stand for?

Answer 7

Initial moles
Change in moles
Equilibrium moles

Question 8

How do you use ICE? MUST PRACTICE

Answer 8

-calculate initial moles of reactant
-the initial moles of product is zero
-calculate equilibrium moles of product
-knowing the equilibrium moles of products, calculate the change in moles
-knowing the change in moles, calculate the equilibrium mole of the other compounds. (times the reactants by minus the change in moles of products)
-use equilibrium moles to calculate concentration

Question 9

How do you use the value of Kc to find equilibrium concentrations? MUST PRACTICE

Answer 9

-substitute
-rearrange
-assume the different compounds hold the same concentration

Question 10

What is total pressure?

Answer 10

sum of all the pressures of the individual gases (partial pressure)

Question 11

How do you calculate total pressure? MUST PRACTICE

Answer 11

total pressure= pressure of reactants + pressure of products
-molar ratios can be used to calculate partial pressures but they must be on the same side of the reversible reaction

Question 12

What is a mole fraction of a gas?

Answer 12

proportion of a. age in a gas mixture

Question 13

How do you calculate the mole fraction of a gas?

Answer 13

number of moles of gas/ total number of moles of gas in the mixture

Question 14

How do you calculate partial pressure?

Answer 14

mole fraction of gas (times) total pressure in mixture

Question 15

what are the units for partial pressure?

Answer 15

kPa

Question 16

Describe the Kp equilibria?

Answer 16

-only includes gases
partial pressures of products/ partial pressures of reactants

Question 17

what is le chatelier’s principle?

Answer 17

if a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will move to counteract the change.

Question 18

what is homogenous equilibria?

Answer 18

reactants and products are in the same state

Question 19

Describe the effect of changing concentration on equilibria?

Answer 19

If we increase concentration of products/ reactants, equilibrium will shift to try to reduce concentration. The opposite will happen if concentration decreased. This only happens in homogenous equilibria.

Question 20

Describe the effect of changing pressure on equilibria?

Answer 20

If we increase pressure, equilibrium will shift to the side with fewer number of gas particles which will reduce the pressure. The opposite will happen if pressure decreased. This only happens in homogenous equilibria.

Question 21

Describe the effect of changing temperature on equilibria?

Answer 21

Increasing temperature will shift equilibrium in the endothermic direction which will reduce the temperature. The opposite will happen if temperature decreased. This only happens in homogenous equilibria.

Question 22

what is the effect of catalysts on equilibria?

Answer 22

-no effects on the position of equilibria
-the rate of the forward and backward reaction will be increase equally
-will speed up the rate at which equilibrium is reached but have no effect on the yield

Question 23

how does temperature affect Kp?

Answer 23

-if temperature change causes equilibrium to shift to the right, Kp will increase
-if temperature change causes equilibrium to shift to the left, Kp will decrease

Question 24

how does changes in pressure and catalyst affect Kp and Kc?

Answer 24

Both have no effect on the value of Kp and Kc

Question 25

how does temperature affect Kc?

Answer 25

-if temperature change causes equilibrium to shift to the right, Kc will increase
-if temperature change causes equilibrium to shift to the left, Kc will decrease