2.1 thermochemistry

Question 1

what is an exothermic reaction?

Answer 1

heat energy is given out to the surroundings.

Question 2

what is an endothermic reaction?

Answer 2

heat energy is taken in from the surroundings.

Question 3

what is the ΔH value of an exothermic reaction?

Answer 3

negative.

Question 4

what is the ΔH value of an endothermic reaction?

Answer 4

positive.

Question 5

what is enthalpy change?

Answer 5

the amount of heat given out or absorbed in a reaction carried out at standard pressure.

Question 6

what are standard conditions?

Answer 6

all elements in their standard states, 298K temperature (25°C), 1 atm pressure (101,000 Pa).

Question 7

what is enthalpy of formation?

Answer 7

the enthalpy change when one mole of a compound is produced from its constituent elements in their standard states.

Question 8

what is enthalpy of combustion?

Answer 8

the enthalpy change when one mole of a substance is completely burned in excess oxygen under standard conditions.

Question 9

what are the products of combustion?

Answer 9

CO2 and H2O.

Question 10

what does hess’ law state?

Answer 10

the enthalpy change of a reaction is independent of the route of the reaction.

Question 11

what is average bond enthalpy?

Answer 11

the energy required to break one mole of a bond in a gaseous species under standard conditions.

Question 12

what is bond enthalpy?

Answer 12

the enthalpy needed to break one mole of the bond to give separated atoms with everything being in the gaseous state.