Enthalpy and entropy

Question 1

what is entropy (S)

Answer 1

entropy is a measure of energy dispersal and disorder within the chemicals making up the chemical system

Question 2

what are the units for entropy

Answer 2

JK-1mol-1 ( joules per kelvin per mol)

Question 3

what happens as entropy increases

Answer 3

as entropy increases , dispersal of energy increases and the system is becoming more disordered

Question 4

is S ( entropy) a positive , negative or either number

Answer 4

S , entropy is always a positive number

Question 5

what is delta S

Answer 5

delta S describes the change in entropy during a chemical reaction

Question 6

what is the trend with entropy

Answer 6

there is a general trend towards greater entropy

Question 7

what is the standard entropy , S0

Answer 7

the standard entropy of one mole of a substance under standard conditions

Question 8

what happens to entropy as temperature increases

Answer 8

entropy increases

Question 9

what will the entropy change be if entropy is increasing and a system is becoming more disorderd

Answer 9

entropy change would be positive

Question 10

what will the entropy change be if entropy is decreasing and a chemical system is becoming more ordered

Answer 10

entropy change would be negative

Question 11

what are the two things to look out for when describing if entropy change is positive or negative

Answer 11

• the number of moles of product vs reactant
• the state of the product vs the reactant

Question 12

how do you calculate the entropy change of a reaction

Answer 12

the standard entropy change of the products - reactants

Question 13

what makes a reaction occur

Answer 13

this depends on whether a reaction is feasible or not. a reaction is feasible

Question 14

what happens to the enthalpy content the chemical system in an exothermic reaction

Answer 14

the enthalpy content decreased during the reaction and excess energy is released to the surroundings , this increases stability

Question 15

what happens to the enthalpy content of a chemical system , in an endothermic reaction

Answer 15

the enthalpy content of the chemical system increases and increase in stability

Question 16

what is delta H

Answer 16

delta H is the heat transfer between the chemical system and the surroundings

Question 17

what determines whether a reaction is feasible or not

Answer 17

the temperature in kelvin
the entropy change in the system
the enthalpy change with the surroundings

Question 18

what is the gibbs equation

Answer 18

the gibbs equation is the free energy change which is known as delta G
delta G = delta H - T ( delta S)
the gibbs equation tells us whether a reaction is going to be feasible or not.
if a reaction is feasible delta G will be negative . and if a reaction is not feasible delta G will be positive

Question 19

what are the units for delta G

Answer 19

KJmol-1

Question 20

what must you remember to do when using the gibbs equation

Answer 20

convert delta S units from joules to kilojoules

Question 21

how to convert degrees to kelvin

Answer 21

+ 273

Question 22

what is the free energy change ( also known as delta G)

Answer 22

the free energy change is the net driving force that determines whether a chemical reaction takes place

Question 23

how do you calculate the minimum temperature at which a reaction becomes feasible

Answer 23

delta H/ delta S
this is because a reaction becomes feasible when delta G is zero

Question 24

what are the limitations of using free energy to predict whether a reaction will actually happen or not

Answer 24

the reaction might have a large activation energy . this will prevent it from happening at a particular temperature

Question 25

what occurs when a reaction is feasible

Answer 25

for a reaction to be feasible there must be a decrease in free energy