equilibrium - unit 3 AOS 2

Question 1

rate vs extent of a reaction

Answer 1

• rate is how much product id formed over a given period of time
• extent is the proportion of reactants that are converted into products

Question 2

yield of a reaction

Answer 2

• yield is the amount of product that is obtained in a chemical reaction.

percentage yield = actual yield/theoretical yield x 100

Question 3

dynamic equilibrium

Answer 3

• the rate of the forward reaction os equal to the rate of the reverse reaction
• there is not net change in reactants and products - they are produced at the same rate
• the concentrations of reactants and products remain constant but not necessarily equal

Question 4

equilibrium constant K

Answer 4

• K is the value that gives an indication of the extent of a chemical reaction
• the larger the value of K, the more the reaction has proceeded.
• large K values indicate that the reaction proceeded significantly
• small K values indicate that the reaction only proceeded moderately.
• the only variable that will change the value of K is the temperature.

Question 5

mixing reactants

Answer 5

• if reactants are mixed, the initial rate of the forward reaction will be greater than the reverse reaction
• at it decreases, the reverse reaction will increase until they are equal

Question 6

homogenous reaction

Answer 6

the reaction occurs entirely within the same physical state

Question 7

heterogenous reaction

Answer 7

a reaction that occurs between two physical states

Question 8

equilibrium law

Answer 8

• the value of K is the ratio of the concentrations of the products to the concentrations of the reactions

Question 9

calculating the K value

Answer 9

K= [products] / [reactants]

Question 10

reverse reactions

Answer 10

• the value of K will be the reciprocal of the forward reaction
• In general, multiplying all reaction coefficients by 𝑥 causes K (and its unit) to be raised to the power of 𝑥.

Question 11

coefficients changing

Answer 11

• In general, multiplying all reaction coefficients by 𝑥 causes K (and its unit) to be raised to the power of 𝑥.

Question 12

using stoichiometry (nICE tables)

Answer 12

n= mole ratio
i = initial concentration
c= change in concentration
e= equalibrium concentration

steps
1. add mole ratios
2. add initial concentrations
3. use stoichiometry to calculate changes in concentration (products will be positive changes, reactants will be negative changes)
4. calculate equilibrium concentrations (initial - change)

Question 13

reaction quotient

Answer 13

• a quantitative measure of how far towards completion a reaction has gone.
• if Q=K, the reaction is at equilibrium
• if Q is greater than K, the reverse reaction id favoured and more products will be converted into reactants
• if Q is less than K, the forward reaction is favoured and more reactants are converted into products.
• the higher the value of Q, the more products there are compare to reactants.

Question 14

Le Chatliers Principle

Answer 14

• when a system at dynamic equilibrium is subject to change, the system will move to counteract this change and restore the system to equilibrium

Question 15

adding reactants

Answer 15

• the forward reaction will be favoured and the reaction will shift to the right, creating more products to partially oppose the increase in reactants.

Question 16

removing reactants

Answer 16

• the reverse reaction will be favoured and it will shift to the left, to partially oppose the decrease in reactants.

Question 17

adding products

Answer 17

• the reverse reaction will be favoured, shifting to the left, to partially oppose the addition of products

Question 18

removing products

Answer 18

• the forward reaction will be favoured, shifting to the right to partially oppose the decrease in products

Question 19

changes to pressure/volume

Answer 19

• in increase in volume will decrease pressure
• a decrease in volume will increase pressure
• an increase in pressure causes the system to shift to the side will fewer particles, to oppose this increase in pressure
• a decrease in pressure will cause the system to shift to the side with more particles.

Question 20

changes in temperature - exothermic reactions

Answer 20

• an increase in temperature causes the reverse reaction to be favoured, shifting to the left and the equilibrium constant will will decrease
• a decrease in temperature, causes the forward reaction to be favoured, shifting to the right and the equilibrium constant will increase

Question 21

changes in temperature - endothermic

Answer 21

• an increase in temperature causes the forward reaction to be favoured, shifting to the right and the equilibrium constant will increase
• a decrease in temperature will cause the reverse reaction to be favoured, shifting to the left and the equilibrium constant will decrease.

Question 23

the conflict between optimal rate and temperature

Answer 23

• increasing temperature increases the rate of reaction for most reactions
• however, for some reactions (exothermic reactions) the yield is higher when the temperature is lower
• therefore conditions need to be comprimised to ensure
• using high temperatures to produce a high rate and lower yield is more economically viable

Question 24

using catalysts

Answer 24

• catalysts can be used to minimise the conflict between rate and temperature.
• catalysts only affect the rate and not the yield
• catalysts can be used to increase the rate of reaction for systems that require low energy for a higher yield to be produced.

Question 25

how can an equilibrium system be made more efficient.

Answer 25

• The use of catalysts to increase the rate of reactions in industrial processes,
  instead of high reaction temperatures. This dramatically reduces energy input, serving both an economic and environmental purpose; lower temperatures are less expensive and require less fuel to maintain
• The use of heat exchangers to recover wasted heat from exothermic reactions
  carried out on a large scale. This Transfers heat from one place to another, so heat energy given off by a reaction can be recovered and reused to continue powering the reaction, thereby reducing energy input requirements.

Question 26

problems with high pressure

Answer 26

• expensive
• explosive

Question 27

creating green hydrogen

Answer 27

the fuel and source of fuel needs to be green
- not of fossil fuel origin