Feasibility and Kinetics

Question 1

What is the standard enthalpy of formation

Answer 1

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

° means standard state

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

What is entropy ?

Answer 3

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

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

Question 4

What always happens for a spontaneous process ?

Answer 4

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

Question 5

What is a perfect crystal ?

Answer 5

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

Question 6

What are the units for the standard enthalpy of a reaction ?

Answer 6

∆ H° (kJ/mol)

Question 7

What is standard entropy ?

Answer 7

The standard entropy of a substance is the entropy value for the substance in its standard state (S°)

The unit of entropy change is J K^-1 mol^-1

Question 8

What does the change in free energy tell us ?

Answer 8

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