unit 2

Question 1

What is equilibrium

Answer 1

the state attained in a reversible reaction, when the rate of the forward reaction equals the rate of the reverse reaction.
the concentration if the reactants and products are constant.
a catalyst has no effect.

Question 2

the equilibrium constant

Answer 2

aA + bB ⇌ cC + dD

K = [C]^c [D]^d / [A]^a [B]^b

Question 3

calculations involving equilibrium constants

Answer 3

the equilibrium constant has no units
if K >1, equilibrium lies to the right, favouring products
if K<1, equilibrium les to the left, favouring reactants
K gives no indication of rate

Question 4

calculations involving equilibrium constants further points

Answer 4

-the concentrations of pure solids and pure liquids at equilibrium are taken as a contestant and given a value of 1 in equilibrium expression
-the value of K can be affected by changing temps.
-the value of K cannot be affected by changes in pressure or concentration.

Question 5

increasing temp does what to the value of K

Answer 5

increases it

Question 6

if value of K is lower at a higher temp

Answer 6

reaction in exothermic, by lowering temp eq goes right

Question 7

Standard enthalpy of formation (∆Hf)

Answer 7

The enthalpy change involved when one mole of a substance is formed from its elements in their standard states

Question 8

eqn used to calculate standard enthalpy change for a chemical reaction

Answer 8

ΔHf = Σ ΔH products - Σ ΔH reactants

Question 8

what is the value of the enthalpy of formation of an element

Answer 8

0

Question 9

standard state

Answer 9

the standard state of a substance is its most stable form at a pressure of 1atm at a specific temperature usually taken as 298 K or 25c

Question 10

entropy

Answer 10

a measure of the amount of disorder

Question 11

symbol for entropy

Answer 11

S

Question 12

standard entropy

Answer 12

entropy at 298K, 1atm

Question 13

units for standard entropy

Answer 13

JK-1 mol-1

Question 14

the standard entropy for solids

Answer 14

lower compared to liquids and gas

Question 15

link between temp and entropy

Answer 15

as temp goes up entropy goes up

Question 16

at what temp do molecular vibrations stop, giving a substance 0 entropy

Answer 16

0K

Question 17

third law of thermodynamics

Answer 17

at 0k, the particles in a solid are no longer vibrating are perfectly ordered. such a solid is described as a perfect crystal. so entropy of a perfect crystal at 0K is zero

Question 18

predicting an increase/decrease in entropy

Answer 18

negative entropy when the reactants have a gas (high entropy), the products are solid (low entropy)

Question 19

calculating entropy change

Answer 19

ΔS = ΣS prod - ΣSreact

Question 20

feasible reaction

Answer 20

one which tends towards the products.

Question 21

eqn that links Gibbs free energy, enthalpy, entropy and temp

Answer 21

ΔG=ΔH-TΔS

Question 22

if ΔG < 0

Answer 22

reaction is feasible/spontaneous

Question 23

second law of thermodynamics

Answer 23

defines the condition for a feasible reaction.

• for a reaction to be feasible, the total entropy for a reaction is positive

Question 24

Free energy

Answer 24

At eq:
ΔG=0

when ΔG<0:
the forward reaction is feasible, with a greater concentration of products. K>1

when ΔG>0
the reverse reaction is feasible, there is a greater concentration of reactants. K<1

Question 25

reaction mechanism and the rate determining step RDS

Answer 25

The rate of a multi step reaction is determined by the slowest step, the RDS

a reaction mechanism/ rate eqn cannot be determined from an equation alone. the order and rate eqn can only be determined from experimental results.

Question 26

rate depends on

Answer 26

the concentration of reactants in the slow step.