Thermo

Question 1

Define state of equilibrium

Answer 1

Thermodynamic state that ≠ change if external conditions are constant

Question 2

When is a reaction reversible

Answer 2

If successive states differ only infinitesimally from equilibrium

∴ can only be between equilibrium states

(In practice external conditions should be varied v.slowly to achieve this ∵ allows system time to equilibrate under new conditions)

Question 3

Zeroth law of thermodynamics

Answer 3

If 2 systems are in thermal equilibrium w/ 3rd = also in thermal equilibrium w/ each other

(• implies existence of an absolute scale of temp)

Question 4

First law of thermodynamics

Answer 4

E ≠ created/destroyed - only transferring/changed between forms

Question 5

What if V = +ve?

Answer 5

W = -ve

Question 6

What is a state function?

Answer 6

Something that depends on the thermodynamic state of the system = P, E, T, V, entropy

Question 7

What is a path function

Answer 7

Something that depends on how they were applied = heat, W

Question 8

State Hess’ law

Answer 8

Heat evolved in a reaction = only determined by p & r ≠ depend on reaction path/intermediate reactions

Question 9

Kirchoff’s law

Answer 9

Δ heat capacity during a reaction depends only on the heat capacities of p & r

Question 10

Latent heat

Answer 10

Extra heat absorbed/released during a phase change

Question 11

Adiabatic flame

Answer 11

(Theoretical) max temp to which the products can be heated

Question 12

Why would a true flame temp be lower than the adiabatic flame temp?

Answer 12

1) incomplete combustion
2) heat transfer to the surroundings
3) dissociation of products
4) kinetic effects

Question 13

What acc is the flame temp?

Answer 13

Temp of surroundings?

Question 14

Adiabatic process

Answer 14

One in which no heat is transferred
(I.e. Q = 0)

Temp can still change since W

Question 15

How does a heat engine work

Answer 15

Converts heat into W by bringing some substance from a high temp -> low temp

Question 16

Carnot Cycle

Answer 16

Theoretical representation of one type of heat engine, w/ gas as the working substance

= most efficient possible heat engine

Question 17

Explain the four components of a Carnot Cycle

Answer 17

1) reversible isothermal expansion of the gas @ hot temp
2) reversible adiabatic expansion of the gas w/cooling
3) reversible isothermal compression of the gas @ cold temp
4) reversible adiabatic compression of the gas w/heating

Question 18

2nd law of thermodynamics

Answer 18

Entropy of an isolated system can never decrease

Question 19

What are the implications of the 2nd law?

Answer 19

1) heat = only transferred spontaneously from higher T -> lower
2) an isolated system which converts W -> heat = possible : BUT not vice versa since heat ≠ W (contradicts 1st law)

Question 20

How can the total entropy of the universe stay constant ?

Answer 20

If system and surroundings undergo reversible processes

Question 21

What happens if a process is irreversible?

Answer 21

Increase of entropy of universe

• entropy is always created (no known way to destroy entropy)

Question 22

What happens when 2 gases mix? + implication?

Answer 22

• they don’t unmix

- implies there’s entropy associated w/mix

Question 23

What is Gibbs Paradox?

Answer 23

There’s no increase in entropy when identical gases

Question 24

3rd law of thermodynamics

Answer 24

Entropy of a perfect crystal @ absolute zero = 0

Question 25

What is a perfect crystal ?

Answer 25

A perfectly spatially ordered structure i.e. 1 possible configuration

Question 26

State the 2 Carnot’s principles

Answer 26

1) thermal η of all reversible heat engines operating between the same 2 thermal reservoirs = same
2) thermal η of a reversible heat engine > η of an irreversible heat engine operating between the same thermal reservoirs