thermodynamics

Question 1

what is Boyles law?

Answer 1

at a fixed temperature, the volume of gas is inversely proportional to the pressure exerted by the gas

Question 2

what is Charles law ?

Answer 2

a law stating that the volume of an ideal gas at constant pressure is directly proportional to the absolute temperature.

Question 3

what is avogadros principle?

Answer 3

equal volumes of gases under the same conditions contain the same number of molecules.

Question 4

what is the ideal gas equation?

Answer 4

pV = nRT

Question 5

what is the gas constant ? including units

Answer 5

8.3145 J Mol-1 K-1

Question 6

what is 1 bar in pascals?

Answer 6

1 x 10^5 Pa

Question 7

what is the partial pressures equation?

Answer 7

pi = xi . ptotal

Question 8

what is the definition for heat?

Answer 8

The transfer of energy as a result of the temperature difference between the system and its surroundings.

Question 9

what is the definition for work ?

Answer 9

This is the mode of transfer of energy that achieves or utilizes uniform motion of atoms in the surroundings.

Question 10

what is a diathermic wall?

Answer 10

it permits the passage of energy as heat

Question 11

what is an adiabatic wall?

Answer 11

its doesn’t permit the passage of heat as energy, even if there is a temperature diofference across the wall.

Question 12

what is irreversible work ?

Answer 12

when a gas expands against a constant external pressure.

Question 13

what is the equation for irreversible work?

Answer 13

work = -pex . deltaT

Question 14

a system in ______ does maximum expansion work

Answer 14

mechanical equilibrium

Question 15

what is reversible work?

Answer 15

when pex = pgas

Question 16

what is the equation for reversible work?

• on equation sheet

Answer 16

work = -nRT . ln(v2/v1)

Question 17

what is the equation for heat capacity ?

• on equation sheet

Answer 17

c = q/deltaT

Question 18

what is the equation for the specific heat capacity ?

• on equation sheet

Answer 18

Cs = q/m deltaT

Question 19

what is the equation for the molar heat capacity ?

• on equation sheet

Answer 19

cm = q/ n deltaT

Question 20

what is the internal energy (U)?

Answer 20

the sum of all the kinetic and potential contributions to the energy of all the atoms, ions, and molecules in the system.

Question 21

when there is a change in volume how do you calculate the change in internal energy

Answer 21

deltaU = q + w

Question 22

for an isolated system q and w =

Answer 22

0 , therefore the internal energy of an isolated system is constant

Question 23

when there is constant volume how do you measure the change in internal energy

Answer 23

deltaU = q

Question 24

what is the equation for a change in enthalpy

• on equation sheet

Answer 24

deltaH = deltaU + p . deltaV

Question 25

what is the enthalpy of vaporisation ?

Answer 25

the energy that must be supplied as heat at constant pressure to convert 1 mole of liquid into the gaseous phase

Question 26

what is the equation for the enthalpy of vaporisation?

Answer 26

deltavapH = qp/n

• small p

Question 27

what is the enthalpy of fusion?

Answer 27

the energy that must be supplied as heat at constant pressure to convert 1 moles of a solid to the liquid phase.

Question 28

what is sublimation

Answer 28

the direct conversion of a solid to a vapour

Question 29

enthalpy of sublimation =

Answer 29

enthalpy of fusion + enthalpy of vaporisation

Question 30

what is combustion

Answer 30

when a substance reacts with oxygen

Question 31

what is Hess’s Law

Answer 31

the total enthalpy change during the complete course of a chemical reaction is independent of the sequence of steps taken.

Question 32

what’s the equation for entropy change ?

Answer 32

deltaS = q(rev) / T

Question 33

what the equation of entropy change accompanying reversible expansion?

Answer 33

deltaS = nR ln(v1/v2)

Question 34

what is the equation for entropy change accompanying a phase transition?

Answer 34

deltaS = deltaHtr / Ttr

tr = the transition of interest
- we use delta H as when at constant pressure qrev = deltaH

Question 35

what does Troutons rule show us

Answer 35

that the change in entropy accompanying vaporisation is the same for all liquids at their boiling temperatures.
this is around +85 J K-1 mol-1

Question 36

if a compound has _____ bonding then it becomes an exception to Troutons rule

Answer 36

hydrogen

Question 37

what is the equation for entropy when accompanying heat

Answer 37

deltaS = C ln (T2/T1)

where C is the heat capacity of the substance of interest

Question 38

for entropy of mixing we note that each gas has performed an ______ expansion.

Answer 38

isothermal, reversible

Question 39

what is the equation for the entropy of mixing

Answer 39

= -R , sum(xi . ln(xi))

Question 40

what is the equation for Gibbs energy change

Answer 40

deltaG = deltaH - TdeltaS

Question 41

what is the difference between deltaGstandard and deltaG ?

Answer 41

The change in Gibbs free energy is under the conditions of the reactants. Whereas the change in Gibbs free energy of pure, unmixed products and reactants under standard conditions, is at the specified temperature and the pressure of one bar.

Question 42

what’s the equation for finding the change in Gibbs energy at a given point during a reaction? (when mixing is occurring)

Answer 42

deltarG = deltarGstandard + RT ln(Q)

where Q is the reaction quotient

Question 43

a system comes to equilibrium when it reaches ____

Answer 43

its minimum Gibbs energy

Question 44

at equilibrium deltaG =

Answer 44

0

therefore 0 = deltarGstandard + RT ln(K)

(swapping Q for K as its at equilibrium.)