# 5.2.2 Enthalpy And Entropy Flashcards

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1
Q

What is entropy?

A

A measure of the dispersal of energy in a system or the degree of disorder.

2
Q

What is standard entropy?

A

Entropy of 1 mole of a substance under standard conditions.

3
Q

What are the units for standard entropy change?

A

JK-1mol-1

4
Q

When is ΔS positive?

A

When a system becomes more disordered, so entropy increases.

5
Q

Examples of entropy increase?

A
• Change of state from solid to liquid/gas.
• Dissolving solid lattice to form solution.
• Reactions where there is an increase in the number of moles of gas.
6
Q

When are reactions more stable?

A

When there is more disorder, so particles will try to move and increase entropy.

7
Q

How come some reactions are feasible even if they are endothermic?

A

To become more energetically stable as ΔS is positive.

8
Q

What is it called when a substance reaches max entropy state?

A

Thermodynamically stable.

9
Q

What is ΔS when a system becomes less disordered?

A

-ve.

10
Q

How do you calculate ΔS?

A

Sum of entropy of the products - sum of entropy of the reactants.

11
Q

What do you need to remember to do to ΔS to use it in another equation?

A

Convert to kJ

12
Q

A

ΔG = ΔH - TΔS

13
Q

What is T measured in?

A

Kelvin.

14
Q

When are reactions always feasible?

A

When ΔH is negative and ΔS is positive.

15
Q

When are reactions never feasible?

A

When ΔH is positive and ΔS is negative.

16
Q

What does ΔG have to be for a reaction to be feasible?

A

Negative.

17
Q

How can you find the max/min temperatures for a reaction to be feasible?

A

Make ΔG = 0

18
Q

What are the limitations of using ΔG to predict feasibility?

A

Activation energy - as if too high reaction won’t occur.

Rate of reaction - if the rate is too slow reaction won’t happen.