thermodynamics

Question 1

what is an isolated system

Answer 1

no exchange of matter or energy with surroundings e.g. a vacuum

Question 2

what is a closed system

Answer 2

exchange of heat but not matter with surroundings e.g. the earth

Question 3

what is an em system

Answer 3

exchange of matter and energy with the surroundings

Question 4

difference between intensive/extensive properties

Answer 4

intensive - independent on amount id material in the system e.g. T and p
extensive- dependent on the amount of material in the system e.g. V, U, H, S and G

Question 5

what is the first law of thermodynamics

Answer 5

energy is neither created or destroyed but just transformed from one kind to another
change in U= q+w
(energy heat and work)
w is negative when work is done by system and positive when work is done by the system

Question 6

what does the sign q tell us

Answer 6

heat (q) tells the direction of heat transfer
if change in temp in -ve, heat is transferred out and q is -ve (exothermic)
if change in temp is +ve, heat is transferred into substance and q is +ve (endothermic)

Question 7

what is enthalpy

Answer 7

the change in enthalpy (H) of a system is the heat transferred from the surroundings to the system in a constant pressure
change in H=qp
qp is heat at constant pressure
H=U+pv

Question 8

what is heat capacity

Answer 8

Cp- heat required to raise T by one degree
ised to relate change in enthalpy to a chnage in temp at constant pressure.
for infinitesimal changes in temp; dH=CpdT
for larger variations of temp (Cp remains constant); change in H = Cp change in T

Question 9

relationship between enthalpy and heat

Answer 9

if change in enthalpy is positive the hear is absorbed by the system and process is endothermic
if change in enthalpy is negative then heat is released by the system and process is exothermic

Question 10

standard state

Answer 10

the standard state of a substance at a specified temp is its pure form at a pressure of 1 bar

Question 11

what can enthalpy changes also be associated with

Answer 11

enthalpy is a state function and can be measured by heat changes at a constant pressure, enthalpy changes are also associated with a change of state

Question 12

types of standard states

Answer 12

adiabatic- no hear enters or leaves the system therefore q=0

isothermal- no temperature change to change in V=O

Question 13

differences between reversible and irreversible reactions

Answer 13

reversible- small ch ages reverse process, max amount of work obtained, occurs slowly

irreversible- small changes don’t reverse reaction, less than max quantity of work obtained, process occurs rapidly

Question 14

work equation

Answer 14

w=-p2 x change in V

Question 15

what is entropy

Answer 15

entropy (S) is the tendency for energy to spread out in a system of atoms and molecules. amount of disorder is called entropy. (increased disorder increased entropy)
disordered states are more probable than ordered states

Question 16

the change in entropy of a system is given by

Answer 16

change in entropy= SFinal-Sinitial

Question 17

how is entropy a state function

Answer 17

positive values of delta S indicate an increase in disorder

negative values of delta S indicate a decrease in disorder

Question 18

what is the second law of thermodynamics

Answer 18

within the context of entropy, the second law of thermodynamics states that in any spontaneous process, there is always an increase in entropy somewhere in the universe

Question 19

for an isothermal process

Answer 19

change in S = qrev/T

qrev = heat transferred reversibly

Question 20

for a non isothermal process

Answer 20

S=k ln W

k= boltzmanns constant and W = no of says of arranging energy

Question 21

entropy of phase transitions

Answer 21

when a substance melts or boils>increase in disorder> increase in S
able to substitute heat of fusion or heat of vaporisations for qrev
for all phase transition
deltaSTrans= deltaHtrans/Ttrans

Question 22

when processes tend to occurs (system and surroundings)

Answer 22

> 0 tends to occur
<0 tends to occur in reverse direction
0 reversible

Question 23

in order for a reaction to occur spontaneously in a forward direction:

Answer 23

delta Ssys+ delta Ssurr ( entropy of universe) must increase

Question 24

what is the third law of thermodynamics

Answer 24

the enthalpy of all pure crystalline solids at the absolute temperature zero is zero
>i.e. S=0 when T=0K

Question 25

what is Gibbs free energy

Answer 25

Gibbs free energy (G)
energy which is, or can be, available to do work
G=H-TS
shows balance between enthalpy and entropy in determining the direction of a process
delta G= delta H - T delta S

Question 26

thermodynamic criteria for a reaction to occur

Answer 26

delta G is negative (spontaneous)
preferably a large negative value
this will increase heat to the surroundings (entropy eill increase)

Question 27

when process will occur in regards to Gibbs free energy

Answer 27

value of delta G
<0 will occur
>0 will occur in reverse
0 reversible 
when reaction at equilibrium delta G is 0

Question 28

what is chemical potential

Answer 28

the contribution the component makes to the overall G of the system
chemical potential = G/n
so chemical potential is the molar free energy or free energy per mole

Question 29

activities (a)

Answer 29

a enables us to wuantify hoe thr chemical potential of a pure substance chnages when it becomes a component in a mixture
activities are related to concentrations by the activity coefficient (lambda)
ai= lambda i x mi
mi = conc of i

Question 30

chemical equilibrium delta G

Answer 30

delta G = sum of products-sum of reactants

Question 31

k in chemical equilibrium

Answer 31

k less than 1, equilibrium lies to LHS

K greater than 1, equilibrium lies to RHS

Question 32

the van’t hoff reaction isochore

Answer 32

equilibrium constants are temp dependant

Question 33

what can van’t hoff reaction isochore be used for

Answer 33

determine variation of equlibrium constant with T