Module 5 - How Far

Question 1

describe how to calculate units for Kc/Kp

Answer 1

-write out the units into the expression
-cancel out units
-if more units on bottom, move to top via - powers

Question 2

describe how to calculate moles at equilibria

Answer 2

-write mole ratio
-write initial moles
-calculate change in moles
-calculate moles at equilibrium

Question 3

describe how to calculate moles at equilibria at volume that isn’t 1dm^3

Answer 3

-convert to dm^3 if needed
-divide by the volume in the question

Question 4

why is Kp used

Answer 4

-easier to measure pressure in gases than concentration

Question 5

describe the relationship between Kp and Kc

Answer 5

-direct relationship
-as pressure and concentration are proportional

Question 6

define Kp

Answer 6

-similar to Kc, but partial pressure is used in place of concentration

Question 7

example of a Kp expression

Answer 7

p( product) ^
/
p(reactant)^

Question 8

describe the reasons for calculating mole fraction

Answer 8

-the same volume of different gases will contain the same number of moles of gas molecules
-proportional by volume to total volume of gases in a gas mixture

Question 9

equation for mole fraction

Answer 9

mole fraction = number of moles of A / total number of moles in gas mixture (A+B+C)

Question 10

what do all mole fractions add to

Answer 10

1

Question 11

equation for partial pressure

Answer 11

partial pressure = mole fraction A x total pressure

Question 12

define partial pressure

Answer 12

-the contribution the gas makes towards the total pressure
-pressure of all gases=pressure of system

Question 13

what factor changes Kc/Kp in reversible reactions

Answer 13

-temperature

Question 14

describe the effect of temperature on Kp/Kc

Answer 14

-(in exo reaction) if temperature increases, Kp increases
-equilibrium moves in the endothermic direction so moves left
-so the denominator increases and numerator decreases
(inverse for endo reactions)

Question 15

describe the effect of concentration on Kp/Kc

Answer 15

-no change
-initial effect affects the numerator and denominator
-when equilibrium reached the numerator and denominator will change by the same amount as the original change
-effect balanced out so no effect on Kp/Kc

Question 16

describe the effect of pressure on Kp/Kc

Answer 16

-no change
-if pressure increases, the compound with the higher power increases more than the lower power, so Kp increases
-at equilibria, it will move to the side with less molecules, increasing value of compound with a lower power and decreasing value of higher power
-so effect balanced out

Question 17

how should the effect of factors on equilibrium be written

Answer 17

-in terms of numerators and denominators