3.1.10 equilibrium constant Kp for homogenous systems

Question 1

homogenous system

Answer 1

all species in same phase - so in this case all gaseous

Question 2

dynamic equilibrium is

Answer 2

for a reversible reaction, when the concentrations of r/p is constant and the rate of the forward and backward reaction is the same

Question 3

we know that equilibrium position can be affected by concentration, this is the basis of the Kc. what else an it be affected by?

Answer 3

pressure, therefore Kp

more specifically the partial pressures of reactants and products

Question 4

what can the mathematical expression for Kp enable us to do

Answer 4

calculate how an equilibrium yield will be influenced by the partial pressures of R/P.

Question 5

partial pressure of a gas is

equation

Answer 5

the pressure the gas would have if it alone occupied the volume the whole mixture takes up

mole fraction of gaseous species x total pressure = pp(species)

Question 6

mole fraction equation

Answer 6

number of moles of gaseous species / total number of moles of all gases in eqm mixture

Question 7

total pressure of mixture is equal to

Answer 7

all partial pressures of each gas added together

Question 8

how would you write an expression for Kp

Answer 8

Kp = p(products) / p(reactants)

power them to their stoichiometric values

just like Kc

Question 9

units of (partial) pressure

Answer 9

kPa - kilopascals

Question 10

what would you do for heterogenous equilibria?

Answer 10

you only include gases in the Kp expression. Ignore solids, liquids, and aqueous substances.

only include the gaseous substances. any other is left out

watch out for this when doing Qs, look at state symbols

Question 11

what factors affect rate of reaction

Answer 11

catalyst
conc
pressure
temp
surface area

Question 12

of the factors that affect rate of reaction, which affects the equilibrium constant( Kc or) Kp

Answer 12

temperature ONLY

Both the position of equilibrium and the value of Kc or Kp will change if temperature is altered.

Question 13

take this equation (Haber)

(all g)
N2 + 3H2 [reversible] 2NH3

the f reaction is exo

what happens when temp is INCREASED?

Answer 13

shifts to decrease temp
therefore shifts in endo direction
so conc products decreases
so less products
so partial pressure of products decreases

Kp = products/reactants

so if products pp is getting smaller, the value of Kp will decrease

Question 14

what happens to Kp when pressure is changed?

Answer 14

the eqm position will shift because of Le Chatelier’s principle: system will oppose change by shifting in direction of larger/less moles of gas

however the eqm constant Kp will not change: the system opposes the change as detailed above. so lets say if pressure increased and products have less gas moles, then position shifts to products. but if reactants have more moles than the pressure increase affects them more , they are decreased in conc and pp as get used up to form products. then products increases (and r decreases) until original value of Kp is restored

Question 15

eqm constant

eqm position

Answer 15

Equilibrium position: a particular set of concentrations of reactant and product species.

Equilibrium constant: a number that describes how far “forward” equilibrium lies for a particular system (as described by a particular equation).

Question 16

why does the position move, for a reason deeper than le chatelier

Answer 16

The position of equilibrium moves - not because Le Chatelier says it must - but because of the need to keep a constant value for the equilibrium constant.