2.1 Thermochemistry

Question 1

How do we calculate overall enthalpy change (ΔH)?

Answer 1

ΔH = energy to break bonds - energy to form bonds

Question 2

Define enthalpy change of formation (ΔHf)

Answer 2

The enthalpy charge when one mole of substance is produced from its constituent elements in their standard state under standard conditions

Question 3

Define enthalpy change of combustion (ΔHc)

Answer 3

The enthalpy charge when one mole of substance is burned completely in oxygen under standard conditions

Question 4

How do you calculate ΔHc?

Answer 4

Sum of products - sum of reactants

Question 5

How do you calculate ΔHf?

Answer 5

Sum of reactants - sum of products

Question 6

If the overall enthalpy (ΔHr) value is negative what type of reaction is it?

Answer 6

Exothermic

Question 7

If the overall enthalpy (ΔHr) value is positive what type of reaction is it?

Answer 7

Endothermic

Question 8

Define bond enthalpy

Answer 8

Energy required to break one mole of the stated bond in its gaseous state under standard conditions

Question 9

How do we find energy change in a reaction?

Answer 9

q = mcΔT

Question 10

How can enthalpy change per mole be calculated?

Answer 10

ΔH = q / moles

Question 11

What does Hess’ law state?

Answer 11

Enthalpy change of a reaction is independent of the route of the reaction