9.1 enthalpy

Question 1

4 standard enthalpy changes

Answer 1

Standard enthalpy change of reaction (ΔrHθ):

Standard enthalpy of combustion : ΔcHθ

Standard enthalpy of formation : ΔfHθ

Standard enthalpy of neutralisation : ΔneutHθ

Question 2

Standard enthalpy change of reaction (ΔrHθ):

Answer 2

is the enthalpy change when the reaction occurs in the molar quantities expressed in a chemical equation under standard conditions,

Question 3

Standard enthalpy of combustion : ΔcHθ

Answer 3

is the enthalpy change that takes place when one mole of a substance reacts/burns completely in oxygen under standard conditions,

Question 4

Standard enthalpy of formation : ΔfHθ

Answer 4

is the enthalpy change that takes place when one mole of a compound is formed from its elements in their standard states under standard conditions.

Question 5

Standard enthalpy of neutralisation : ΔneutHθ

Answer 5

is the energy change when an acid and a base react to form 1 mole of water under standard conditions

Question 6

enthalpy CHANGE (ΔH) formula

Answer 6

ΔH = Hproducts - Hreactants

Question 7

first law of thermodynamics

Answer 7

the CONSERVATION OF ENERGY.

Energy cannot be created or destroyed just transferred between the
system and the surroundings.

Question 8

Draw exothermic energy profile diagram

Answer 8

An exothermic reaction means that the enthalpy content of the products is smaller
than the reactants.

The excess energy is transferred from the system to the surroundings so the
temperature of the surroundings increases.

Question 9

5 examples of exothermic reactions

Answer 9

1) Oxidation of fuels

2) Respiration:

An important exothermic reaction providing energy for all living things:

C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) ΔH = -2801 kJ mol-1

3) Neutralisation

4) Hand warmers

5) Rusting

Question 10

draw an endothermic energy profile diagram

Answer 10

An endothermic reaction means that the enthalpy content of the products is
greater than the reactants.

The excess energy is transferred to the system from the surroundings resulting in a temperature decrease.

Question 11

5 examples of endothermic reactions

Answer 11

1) Photosynthesis:

2) Thermal decomposition of limestone:

3) Cracking of alkanes

4) Ice packs

5) Baking bread

Question 12

define activation energy

Answer 12

activation energy is the minimum energy needed to start a reaction by
breaking bonds.Ea

Question 13

what are the four standar conditions

Answer 13

Pressure at 100 kPa (1 atmosphere is 101kPa)

Temperature at 298K (25oC)

1 Mole solid or 1 Molar solutions

Normal physical states at standard temperature and pressure

Question 14

standard enthalpy change is represented with what symbol and its units are?

Answer 14

ΔHθ

H - Enthalpy

Δ - Change in

θ - symbol represents standard conditions

• UNITS = kJmol-1

Question 15

Enthalpy change

Answer 15

is the heat energy transferred in a reaction at a constant pressure. units KJ mol-1

Question 16

Exothermic reactions give out energy the enthalpy change is

Answer 16

negative

Question 17

Endothermic reactions give out energy the enthalpy change is

Answer 17

positive

Question 18

how are enthalpy and stability related?

Answer 18

the lower the enthalpy the more stable a substance is