Reaction Feasibility

Question 1

What is the standard enthalpy of formation

Answer 1

The standard enthalpy of formation, ∆ ° H f , is the enthalpy change when one mole of a
substance is formed from its elements in their standard states.

Question 2

What is the standard state of a substance

Answer 2

The standard state of a substance is its most stable state at a pressure of 1 atmosphere
and at a specified temperature, usually taken as 298 K.

Question 3

The standard enthalpy of a reaction can be calculated from the standard enthalpies of
formation of the reactants and products:

Answer 3

Delta H =E^H (products) - E^H (reactants)

Question 4

What is the entropy of a system the measure of

Answer 4

The entropy (S) of a system is a measure of the degree of disorder of the system.

Question 5

The greater the degree of disorder…

Answer 5

The greater the degree of disorder, the greater the entropy.

Question 6

What is the difference in disorder of solids and gases

Answer 6

Solids have low disorder and gases have high disorder.

Question 7

What does entropy increase with

Answer 7

Entropy increases as temperature increases.

Question 8

What happens to the rate of entropy at the melting and boiling point of a substance

Answer 8

There is a rapid increase in entropy at the melting point of a substance and an even more rapid and larger change in entropy at the boiling point.

Question 9

What does the second law of thermodynamics state

Answer 9

The second law of thermodynamics states that the total entropy of a reaction system and its surroundings always increases for a spontaneous process.

Question 10

What is the effect of heat energy released to the surroundings

Answer 10

Heat energy released by the reaction system into the surroundings increases the entropy of the surroundings.

Question 11

What happens when energy is absorbed by the reaction system

Answer 11

Heat energy absorbed by the reaction system from the surroundings decreases the entropy of the surroundings.

Question 12

What does the third law of thermodynamics state

Answer 12

The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is zero.

Question 13

What is the standard entropy of a substance

Answer 13

The standard entropy of a substance is the entropy value for the substance in its standard state.

Question 14

The change in standard entropy for a reaction system can be calculated from the standard entropies of the reactants and products:

Answer 14

AS=ES°(products) - ES°(reactants)

Question 15

The change in free energy for a reaction is related to the enthalpy and entropy changes:

Answer 15

ΔG° = ΔH° - T ΔS°

Question 16

What happens if the change in free energy between reactants and products is negative

Answer 16

f the change in free energy ( ∆ ° G ) between reactants and products is negative, a reaction
may occur and the reaction is said to be feasible

Question 17

What is a feasible reaction

Answer 17

A feasible reaction is one that tends
towards the products rather than the reactants. This does not give any indication of the rate of the reaction.

Question 18

How can the standard deee energy change for a reaction be calculated

Answer 18

The standard free energy change for a reaction can be calculated from the standard free energies of formation of the reactants and products using the relationship:
∆G° = Σ∆G° (products) − Σ∆G° (reactants )

Question 19

How can the feasibility of a chemical reaction under standard conditions be predicted

Answer 19

The feasibility of a chemical reaction under standard conditions can be predicted from the calculated value of the change in standard free energy ( ∆ ° G ).

Question 20

How can the temperature at which a reaction may be feasible be estimated

Answer 20

The temperatures at which a reaction may be feasible can be estimated by considering the range of values of T for which ∆ °< G 0 .

Question 21

What is any reaction under non standard conditions

Answer 21

Under non-standard conditions any reaction is feasible if ∆G is negative.

Question 22

What does ∆G° = at equilibrium

Answer 22

At equilibrium ∆G° = 0

Question 23

How will a reversible reaction proceed

Answer 23

A reversible reaction will proceed spontaneous until the composition is reached where ∆G=0