3.1.6 equilibria

Question 1

what does completion mean?

Answer 1

they continue until all the reactants are used up, then the reaction stops

Question 2

What are the reactions called that do not go to completion?

Answer 2

reversible reactions

Question 3

what is the chemical equilibrium reached?

Answer 3

A chemical equilibrium is reached in a reversible reaction with the rate of the forward reaction is equal to the rate of the reverse reaction

Question 4

What is dynamic equilibrium?

Answer 4

rate of the forwards and backwards reactions are equal and the concentration remains constant

Question 5

what can chemical equilibria either be?

Answer 5

homogeneous or heterogeneous

Question 6

what are characteristics of a dynamic equilibrium?

Answer 6

• A dynamic equilibrium can only occur in a closed system
• reactions continue to occur - the reaction is dynamic
• The concentrations of reactants and products remain constant
• The equilibrium can be established from either side of the reaction

Question 7

what is a closed system?

Answer 7

No more reactants are added, and no reactants are removed

as the pressure of the system is constant

Question 8

what are the three factors that affect the position of an equilibrium?

Answer 8

Temperature, pressure and concentration

Question 9

what does Le Chatelier’s principle state?

Answer 9

A system at equilibrium will shift to oppose any change imposed upon it

Question 10

Is the position of a chemical equilibrium affected by a catalyst?

why?

Answer 10

No

catalysts speed up the forwards and backwards reactions equally

Question 11

If the concentration of one of the reactants is increased, what will happen to the equilibrium?

Answer 11

The position of the equilibrium will shift to oppose the change

Question 12

pressure only affects the position of chemical equilibria that involve what?

Answer 12

Gases

Question 13

if the pressure is increased equilibrium that the position of the equilibrium moves, where?

Answer 13

To the sides of the reaction with fewer gaseous moles

as this reduces the pressure of the gaseous system

Question 14

where the temperature of a reaction is increased, what reaction is favoured, and why?

Answer 14

The endothermic reaction is favoured

As this remove the added heat also opposes the increase in temperature

Question 15

where the temperature of reaction is decreased, what reaction is favoured? why?

Answer 15

The exothermic reaction is favoured

As this releases, heat, energy and opposes the decrease in temperature

Question 16

what are the optimum conditions for the Haber process?

Answer 16

• The forward reaction, producing ammonia is exothermic, answer releases, heat, energy
• Applying Le Chatelier’s principle, this is favoured by lower temperatures as this will shift the equilibrium to the right and increase the yield of ammonia at equilibrium

Question 17

what temperatures and pressures are the best yields obtained at?

Answer 17

very low temperatures and very high pressures

Question 18

at …….. temperatures, the reaction rate is …….. and although the ………. of product is better, the rate of …………. is too slow to be ……… …………….

Answer 18

low
slow
yield
production
cost effective

Question 19

what conditions do industrial chemists use that produce an acceptable yield an acceptable rate?

Answer 19

compromise conditions

Question 20

what are two important chemicals that are increasingly finding use as fuels?

Answer 20

ethanol and methanol

Question 21

what’s the chemical formula for ethanol?

Answer 21

C2H5OH

Question 22

ethanol is prepared by the hydration of what?

Answer 22

Ethene

Question 23

what is Kc?

Answer 23

A ratio of the concentration of the products to reactants at equilibrium

Question 24

does the left side or right side of an equation go on the top when writing Kc values?

Answer 24

right

Question 25

why do catalysts have no effect on the position of equilibrium or on the value of Kc?

Answer 25

because catalysts increase the rate of both the forward and reverse reactions equally

As a result, the equilibrium position is unaltered but equilibrium will be achieved faster

Catalysts can’t increase the yield of a product, but they do decrease the time taken to achieve equilibrium