Thermodynamics (w7)

Question 1

What are the 4 forms of potential energy ?

Answer 1

• gravitational (a raised weight)
• elastic (a stretched rubber band)
• chemical (a charged battery)
• electrical (a mobile phone which is switched off)

Question 2

Define potential energy …

Answer 2

Any form of stored energy

Question 3

What are the 5 forms of kinetic energy ?

Answer 3

• radiant (electric toaster)
• thermal (boiling water)
• sound (buzzing bee)
• electrical (desk lamp)
• mechanical (bowling ball rolling)

Question 4

Define kinetic energy …

Answer 4

The energy of moving objects.

Question 5

What is a system ?

Answer 5

The substance in the flask

Question 6

What are the three types of system ?

Answer 6

-closed system
-open system
-isolated system

Question 7

What is the zeroth law of thermodynamics ?

Answer 7

“If two systems are in thermal equilibrium with a third system, the two original systems are in thermal equilibrium with each other”

Question 8

What is the first law of thermodynamics?

Answer 8

“Energy cannot be created or destroyed – it can only be transformed from one form to another”

Question 9

What is the law of conservation of energy ?

Answer 9

“The change in internal energy of a closed system will be equal to the heat added or released by the system minus the work done by the system on its surrounding or the work done on the system by its surroundings”

Question 10

What is the equation for the first law of thermodynamics ?

Answer 10

Delta U = Q - W

Change in internal energy = heat added to the system - work done by the system

Question 11

What does it mean when the volume is constant ?

Answer 11

It is isovolumetric
-delta U = q
-no works done on or by the system
-any energy change is a result of heat transfer

Question 12

What does is mean if there is a constant temperature ?

Answer 12

It is isothermal
-q = w
- no change in internal energy
- any heat transferred to system is used to do work

Question 13

What does it mean if no heat is transferred ?

Answer 13

It is adiabatic
-delta A = W
- internal energy changed only for work Dione or received by the system.

Question 14

Define heat capacity …

Answer 14

Heat Capacity (C): amount of heat required to raise a substance’s temperature by 1 Kelvin

Question 15

Define specific heat capacity …

Answer 15

Specific Heat Capacity (Cₛ): amount of heat required to raise 1 gram of a substance by 1 Kelvin

Question 16

What is an endothermic process ?

Answer 16

When energy is gained
(Temp of unit increases so deltaH is POSITIVE)

Question 17

What is an exothermic process ?

Answer 17

When energy of unit is lost to surroundings
(It looses energy so temp decreases, deltaH is NEGATIVE)

Question 18

What is the second law of thermodynamics ?

Answer 18

‘’ the universe is always moving towards the maximum disorder’’

Question 19

What happens if there is an increase in the number of microstates ?

Answer 19

The entropy of the system increases (Wf>Wi)
So deltaS >0.

Question 20

What happens if there is a decrease in the number of microstates ?

Answer 20

The entropy of the system will decrease (Wf<Wi) so deltaS<0.

Question 21

What is the order of entropy for states ?

Answer 21

Solid < liquid < gas

E.g melting solid increases entropy then Vaporising this increases entropy even more.

Question 22

What effect does increasing temperature have on entropy ?

Answer 22

The entropy will be greater as molecules gave more kinetic energy and therefore more dispersion.

Question 23

What effect does mixing of particle types have on entropy ?

Answer 23

It increases the entropy therefore dissolution increases entropy.

Question 24

What is the third law of thermodynamics ?

Answer 24

“At absolute zero (0 K), the entropy of a perfect, crystalline substance is zero”

Question 25

When does a system come to equilibrium ?

Answer 25

When it reaches minimum Gibbs energy

Question 26

What does equilibrium constant K describe ?

Answer 26

The composition of a reaction mixture when it comes to equilibrium

Question 27

What is thermodynamic activity ?

Answer 27

Effective measured concentration or pressure of a component at a given moment (equilibrium for k)

Question 28

When is K used ?

Answer 28

In heterogeneous reactions
- when a reaction has more than one phase - instead of using Kc or Kp, K is used.

Question 29

What must K always be associated with ?

Answer 29

A specified temperature and the equation of the reaction being considered.

Question 30

What is the reaction quotient (Q)?

Answer 30

Reaction Quotient Q: Measure of the composition of the reaction mixture as the reaction progresses – not at equilibrium

Question 31

What happens If ∆Gr < 0, Q < K ?

Answer 31

Then the forward reaction proceeds

Question 32

What happens if ∆Gr > 0, Q > K ?

Answer 32

Then the reverse reaction proceeds

Question 33

What happens If ∆Gr = 0, Q = K ?

Answer 33

Then the system is at equilibrium

Question 34

When does a reaction go to completion ?

Answer 34

If delta G is more -ve than -22.8 kj/mol

Question 35

What is Le Chatelier’s principle `/

Answer 35

When a change is made to a system in dynamic equilibrium, the system responds to minimise the effect of the change