Total entropy

Question 1

the total entropy change of a process is comprised of the two componenets:

Answer 1

• entropy change of the system ΔSsystem

- entropy change of the surroundings ΔSsurroundings

Question 2

in a chemical reaction, the system is

the surroundings is

Answer 2

the species that are taking part int he reaction

surroundings is everything else, usually the reaction vessel

Question 3

the total entropy change is defined as

Answer 3

the sum of the entropy change of the system an the entropy change of the surroundings

Question 4

ΔTtotal =

Answer 4

ΔStotal = ΔSsystem + ΔSsurroundings

Question 5

for a reaction to be spontaneous, Δtotal must be

Answer 5

positive

Question 6

ΔSsystem =

Answer 6

ΔSsystem = ΣS(products) - ΣS(reactants)

where S is entropy and Σ means ‘sum of’

Question 7

entropy values usually use the units:

enthalpy values usually use the units:

Answer 7

entropy values usually use the units: J K-1 mol-1

enthalpy values usually use the units: kJ mol-1

Question 8

ΔSsurroundings =

Answer 8

ΔH
ΔSsurroundings = - ——
T
where T is the temp in Kelvin

Question 9

for an exothermic reaction, where ΔH is negative, ΔSsurroundings will be……………….meaning the entropy of the surroundings will ……………………

Answer 9

always be positive

therefore the entropy of the surroundings will increase

Question 10

for an endothermic reaction, ΔSurroundings will always be…………….meaning the entropy of the surroundigns will……………

Answer 10

negative

so the entropy of the surroundings will decerase

Question 11

ΔStotal will be positive if: (3 items)

Answer 11

• both ΔSsurroundings and ΔSsystem are positive
• ΔSsurroundings is positve and ΔSsystem is negative but the magnituude of ΔSsurroundigns is greater than the magnitude of ΔSsystem
• ΔSsystem is positive and ΔSsurroundings is negative, but the magnitiude of ΔSsystem is greater thn th magnitude of ΔSsurrounrings

Question 12

the increase in entropy obtained by supplying a certain amount of heat energy to an object depends on

Answer 12

the temperature of the system

Question 13

if a cold object is heated, then the entropy will……………because the molecules have gone from not…………….to moving……….

Answer 13

increase because the molecules have gone from not moving much to moving a lot

Question 14

if a hotter object is supplied with the same amount heat energy as given to a cold object, then its entropy will increase by…………….

Answer 14

not very much as the molecules are already moving around vigorously and the increased degree of movement is less for the hot object

Question 15

ice has lower entropy tan liquid water, so ΔSsystem is

Answer 15

negative

Question 16

the process of water freezing is…..thermic so ΔSsurroundings is

Answer 16

exothermic so ΔSsurroundings is positive

Question 17

water will freeze when:

balance between ΔSsystem and ΔSsurroundings to create ΔStotal as a positive value

Answer 17

magnitude of ΔSsurroundings > magnitude ΔSsystem

this is because ΔSsurroundings is positive so must be greater in magnitude than ΔSsystem which is negative, in order for ΔStotal to be positive and the process to be spontaneous

Question 18

the reason we put water into a freezer to freeze is because

Answer 18

the entropy change of the surroundings (the air inside the freezer) is large enough to compensate for the decrease in entropy when the water freezes