5.1 Rates, equilibrium and pH

Question 1

What is ‘rate of reaction’?

Answer 1

the speed at which a chemical reaction takes place

Question 2

What does order mean?

Answer 2

the power to which a concentration of a reactant is raised in the rate equation

Question 3

What is a rate constant?

Answer 3

the rate constant, k, is a proportionality constant that links the rate of reaction with the concentration of reactants

Question 4

What is the definition of half-life?

Answer 4

the time taken for the concentration of a reactant to reduce by half

Question 5

What is the rate-determining step?

Answer 5

the slowest step of the reaction, that determines the rate of the whole reaction

Question 6

What are the units for rate of reaction

Answer 6

mol dm-3 s-1

Question 7

How do you calculate rate constant, k?

Answer 7

k = ln(2) / t1/2 (half life(s))

Question 8

Describe a zero order rate-concentration graph

Answer 8

straight horizontal line
y-intercept gives rate constant, k
changes in conc have no effect on rate

Question 9

Describe a first order rate-concentration graph

Answer 9

straight line through origin
rate directly proportional to conc
rate constant is gradient

Question 10

Describe a second order rate-concentration graph

Answer 10

upward curve with increasing gradient - from origin
2nd graph of rate-(conc)^2 drawn to find rate constant - gradient of 2nd line

Question 11

Describe a zero order concentration-time graph

Answer 11

straight line with negative gradient
reaction rate doesnt change
gradient=k
half life decreases

Question 12

Describe a first order concentration-time graph

Answer 12

downwards curve - decreasing gradient
half life is constant - time for reactant to half each time

Question 13

Describe a second order concentration-time graph

Answer 13

downwards curve, steeper at start
half life increases with time

Question 14

How does an increase in temperature affect the rate of reaction and rate constant?

Answer 14

rate increases - boltzsman distribution shifts to the right so more particles overcome Ea
- particles move faster and collide more frequently

Question 15

What is the definition of mole fraction?

Answer 15

a measure of how much of a given substance is present in a reaction mixture

Question 16

What is the equation for mole fraction?

Answer 16

xA = number of moles of substance A / total number of moles

Question 17

What is the definition of partial pressure?

Answer 17

the pressure an individual gaseous substance would exert if it occupied a whole reaction vessel on its own

Question 18

What is the equation for partial pressure?

Answer 18

mole fraction * total pressure

Question 19

Which methods can determine concentrations at equilibrium?

Answer 19

titrations
using a colorimeter

Question 20

How to determine concentrations at equilibrium using a titration?

Question 21

How to determine concentrations at equilibrium using a colorimeter?

Question 22

What is the effect of an increase temperature on Kc

Answer 22

exothermic - Kc decreases
endothermic - Kc increases

Question 23

Does pressure affect Kc?

Answer 23

No

Question 24

What happens to Kc if the concentrations increase?

Answer 24

Kc stays the same as the concentrations will change to restore the original Kc

Question 25

What is the effect of a catalyst on a reaction?

Answer 25

increases rate of forwards and backwards reaction by the same amount lowers activation energy reaction can take place at a lower temperature cheaper

Question 26

What is the effect of increasing pressure on Kc?

Answer 26

increased pressure = increases concentrations so Kc will stay the same as concentrations will change to revert Kc to original

Question 27

What is a Bronston-Lowry acid?

Answer 27

an acid that donates a proton

Question 28

What is a Bronston-Lowry base?

Answer 28

a base that accepts a proton

Question 29

What is the equation to work out pH?

Answer 29

pH = -log [H+]

Question 30

What is the equation that calculates [H+]?

Answer 30

[H+] = 10^ (-pH)

Question 31

What is a conjugate acid-base pair?

Answer 31

a set of 2 species that change into one another by gaining or losing a H+ ion they have a difference of 1 H+ ion

Question 32

What is a mono-basic acid? (give an example)

Answer 32

acid that releases 1 H+ proton e.g. HCl

Question 33

What is a di-basic acid? (give an example)

Answer 33

acid that releases 2H+ protons e.g. H2SO4

Question 34

What is a tri-basic acid? (give an example)

Answer 34

acid that releases 3 H+ protons e.g. H3PO4

Question 35

What type of acid is CH3COOH ?

Answer 35

monobasic acid - the cooh group only counts

Question 36

acid + carbonate

Answer 36

salt + carbon dioxide + water

Question 37

acid + base

Answer 37

salt + water

Question 38

acid + alkali

Answer 38

salt + water

Question 39

(redox) acid + metal

Answer 39

salt + hydrogen

Question 40

What does the acid dissociation constant, Ka show?

Answer 40

the actual extent of acid dissociation measured by an equilibrium constant

Question 41

What is Ka for HA(aq) —— H+ (aq) + A- (aq)

Answer 41

Ka = [A-][H+] / [HA]

Question 42

What does a large Ka value show?

Answer 42

a large extent of dissociation - a strong acid

Question 43

What does a small Ka value indicate?

Answer 43

small extent of dissociation - a weak acid

Question 44

What is the equation to find pKa and Ka?

Answer 44

pKa = -log10(Ka) Ka = 10^(-pKa)

Question 45

What does a large and small pKa value show?

Answer 45

small pKa value - stronger acid high pKa value - weaker acid

Question 46

What does a low pH value show?

Answer 46

a high concentration of H+

Question 47

What does a high pH value show?

Answer 47

a low concentration of H+ ions