Chapter 9 Enthalpy

Question 1

What is activation energy

Answer 1

E_a is the minimum energy required for a
reaction to take place.

Question 2

What are the standard conditions

Answer 2

100 kPa (very close to 1 atm pressure)
- 298 K (25 °C)
- 1 mol dm^-3 – relevant for solutions only
- Standard state – the physical state of a
substance under standard conditions

Question 3

What is the Standard enthalpy change of reaction (∆_rH^θ)

Answer 3

(∆_rH^θ) is the enthalpy
change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions

Question 3

What is the Standard enthalpy change of reaction (∆_rH^θ)

Answer 3

(∆_rH^θ) is the enthalpy
change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions

Question 4

What is Standard enthalpy change of formation (∆_fH^θ)

Answer 4

(∆_fH^θ) is the enthalpy change
associated with the formation of 1 mole of a compound from its elements under standard conditions

Question 5

What is the standard enthalpy of combustion (∆_cH^θ)

Answer 5

(∆_cH^θ) is the enthalpy
change associated with the complete combustion of 1 mole of a substance under standard conditions

Question 6

What is the Standard enthalpy change of neutralisation (∆_neutH^θ)

Answer 6

(∆_neutH^θ) is the enthalpy
change associated with the formation of 1 mole of water from a neutralisation reaction between an acid and a base, under standard conditions.

Question 7

What is the (∆_neutH^θ) for the reaction between a strong acid and a strong base

Answer 7

-57 kJ mol^-1

Question 8

What is the equation for heat energy (q) transferred to the surroundings and what are the units

Answer 8

q = m c ∆T

• Mass - g
• ∆T - Kelvin
• Heat Energy - J

Question 9

How do you convert from °C to K

Answer 9

add 273

Question 10

When conduction an experiment (spirit Burner) to find the standard enthalpy of combustion, why is the experimental value less exothermic

Answer 10

Heat loss to the
surroundings (beaker and
air surrounding the flame)
* Incomplete combustion of
the fuel
* Evaporation of fuel
* Not performed under
standard conditions

Question 11

What is average bond enthalpy

Answer 11

The energy required to break one mole of a specified
type of bond in a gaseous molecule

Question 12

What is the unit for average bond enthalpy

Answer 12

kJ mol^-1

Question 13

How do you calculate enthalpy changes from average bond
enthalpies

Answer 13

Δ_rH = Σ(bond enthalpies in reactants) – Σ(bond enthalpies in products)

Question 14

What is Hess’ law

Answer 14

If a reaction can take place by two routes, and the
starting and finishing conditions are the same, the total
enthalpy change is the same for each route