Oceans 5: Entropy

Question 1

Symbol for entropy

Answer 1

S

Question 2

Definition of entropy

Answer 2

Entropy = quantity ( S ) which represents the degree of disorder in a system

Question 3

Units of entropy

Answer 3

J mol^-1 K^-1

J / mol K

Question 4

What is the relationship between entropy and degree of disorder

Answer 4

Increase entropy = increase degree of disorder

Question 5

Why are entropy values always greater than 0

Answer 5

Due to vibration of movement of particles

Question 6

How does temperature effect entropy

Answer 6

Increase temp = increase entropy

Question 7

What does entropy increase when temperature increases

Answer 7

Because heating generally results in particles becoming more disordered

Question 8

Compare the entropies of a gas, liquid and solid

Answer 8

gas > liquid > solid

Question 9

Compare the entropies of mixtures and deprecate substances ( eg. Pure substance)

Answer 9

mixture > separate

Question 10

Compare the entropies of large molecules & small molecules

Answer 10

larger molecules > smaller molecules

Question 11

What 2 things are higher values of entropy favoured by

Answer 11

1. Spreading out of molecules

2. Higher temp

Question 12

More ordered structure = ??? entropy

Give example of substance with low entropy

Answer 12

more ordered structure = lower entropy

Eg. Diamond & graphite = very low entropy

Question 13

Equation of entropy change ( delta S sys )

sys = system= where reaction takes places ie. beaker / test tube

Answer 13

Delta S sys = sum of PRODUCTS - sum of REACTANTS

Question 14

What does a +ve delta S represent

Answer 14

Increase in entropy

Question 15

What does a -ve delta S represent

Answer 15

Decrease in entropy

Question 16

What kind of reaction are more favoured, increase or decrease in entropy?

Answer 16

Reactions where there is an increase in entropy are more favourable i.e disorder = good

Question 17

How can you predict changes in entropy by looking at an equation

Answer 17

By using

• no. of moles on each side
• state symbols ( be careful when dealing with aqueous compounds = one mol of each ion )

Question 18

Predict whether entropy will increase or decrease from the equation below

• NaCl ( s ) —> NaCl ( aq )

Answer 18

• entropy increases

- 1 mole solid —> 2 mol aq ( 1 mol Na+(aq) + 1 mol Cl-(aq) )

Question 19

Give equation for total entropy change ( delta S total )

Answer 19

delta S total = delta S sys + delta S surr

Total = system + surroundings

Question 20

Give equation for enthalpy change of surroundings (delta S surr)

Answer 20

delta S surr = - delta H / T

• delta H = enthalpy change = Joules ( KJ -> J = x1000 )
• T = temperature = Kelvins ( °c —> K =+273)

Question 21

What conditions are required for a chemical change to be feasible

Answer 21

Delta S total = +ve

Question 22

What does a -ve delta S total tell you about a chemical change reaction

Answer 22

-ve = not feasible

Question 23

When does the minimum temperature for a reaction to be feasible occur

Answer 23

Delta S total = 0

Question 24

Definition of feasible

Answer 24

• Feasible = reaction does occur

- Not feasible = reaction doesn’t occur

Question 25

How do you calculate enthalpy of reaction give enthalpies of formation

Answer 25

Using a Hess cycle ( arrows towards equation )

Delta H1 = -delta H2 +delta H3