thermodynamics

Question 1

what is Boyles law?

Answer 1

The volume of gas is inversely proportional to the pressure at constant temperature.

Question 2

what is Charles law ?

Answer 2

the volume of an ideal gas at constant pressure is directly proportional to the 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?

• on equation sheet

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 internal energy (U)?

Answer 17

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

total energy of a system

Question 18

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

• on equation sheet

Answer 18

deltaU = q + w

Question 19

for an isolated system q and w =

Answer 19

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

Question 20

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

Answer 20

deltaU = q

Question 21

what is the equation for a change in enthalpy, in terms of internal energy.

• on equation sheet

Answer 21

deltaH = deltaU + p . deltaV

Question 22

what is the enthalpy of vaporisation ?

Answer 22

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

Question 23

what is the equation for the enthalpy of vaporisation, for a non constant pressure?

Answer 23

deltavapH = qp/n

Question 24

deltaH = ? at constant pressure

Answer 24

q (heat)

Question 25

what is the enthalpy of fusion?

Answer 25

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

Question 26

what is sublimation

Answer 26

the direct conversion of a solid to a vapour

Question 27

enthalpy of sublimation =

Answer 27

enthalpy of fusion + enthalpy of vaporisation

Question 28

what is combustion

Answer 28

when a substance reacts with oxygen

Question 29

what is Hess's Law

Answer 29

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

Question 30

what's the equation for entropy change ?

Answer 30

deltaS = q(rev) / T

Question 31

what the equation of entropy change accompanying reversible expansion? - on equation sheet

Answer 31

deltaS = nR ln(v1/v2)

Question 32

what is the equation for entropy change accompanying a phase transition, when you have the enthalpy change.

Answer 32

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

Question 33

what does Troutons rule show us

Answer 33

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 34

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

Answer 34

hydrogen

Question 35

what is the equation for entropy when there is a change in temperature. - on equation sheet

Answer 35

deltaS = C ln (T2/T1) where C is the heat capacity of the substance of interest

Question 36

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

Answer 36

isothermal, reversible

Question 37

what is the equation for the entropy of mixing - on eqaution sheet

Answer 37

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

Question 38

what is the equation for Gibbs energy change

Answer 38

deltaG = deltaH - TdeltaS

Question 39

what is the difference between deltaGstandard and deltaG ?

Answer 39

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 40

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

Answer 40

deltarG = deltarGstandard + RT ln(Q) where Q is the reaction quotient

Question 41

a system comes to equilibrium when it reaches ____

Answer 41

its minimum Gibbs energy

Question 42

at equilibrium deltaG =

Answer 42

0 therefore 0 = deltarGstandard + RT ln(K) (swapping Q for K as its at equilibrium.)

Question 43

how do you convert cm^3 to m^3

Answer 43

x10^-6

Question 44

what unit should the v be in when dealing with the ideal gas equation

Answer 44

m^3

Question 45

how do you calculate the enthalpy of vaporisation at a constant pressure

Answer 45

q/n - remove p from the equation - only include p when your measure a specific pressure when the pressure changes.

Question 46

combine work and the ideal gas equation

Answer 46

w = -nRT

Question 47

what unit is entropy measured in

Answer 47

J K-1

Question 48

what K should you add to celsius to covert it

Answer 48

273.15

Question 49

how to convert 1 atm to pa

Answer 49

1 atm = 101325 pa

Question 50

for a isothermal process (constant temperature) the change in internal energy is ...

Answer 50

0, this means that 0 = q + w