Chapter 7.4

Question 1

What is the relation in enthalpy to heat

Answer 1

-change in enthalpy is equal to the heat transferred into or out of the system at constant pressure

Question 2

What does Hess’s law state about enthalpy

Answer 2

• that enthalpy changes of reactions are additive
• > thermochemical equations are added to give the net equation for a reaction and the corresponding heats of reaction are also added to give the net heat of the reaction

Question 3

What are bond dissociation energies? Is bond dissociation an endothermic or exothermic process

Answer 3

• they are the average energy required to break a particular type of bond between atoms in the GAS phase
• > bond dissociation is an endothermic process

-the units for bond dissociation energy is given by the units kJ/mol

Question 4

What is the standard enthalpy of formation

Answer 4

• it is the enthalpy required to produce one mole of a compound from its elements in their standard states
• > standard states is the most stable physical state of an element or compound at 298 K and 1 atm

-the enthalpy of formation for an element in its standard state is zero

Question 5

Does Hess law apply to any state function

Answer 5

• yes

- >including entropy and Gibbs free energy