Enthalipes of combustion

Enthalpy of combustion (ΔHc)

The enthalpy change when 1 mole of a substance is burned completely in oxygen.

Enthalpy of solution (ΔHaq)

The enthalpy change when 1 mole of a substance is dissolved in water until there is no further temperature change.

Enthalpy of neutralisation (ΔHn)

The enthalpy change when 1 mole of water is formed by an acid being neutralised by a base.

Eh = c mΔT

The equation used to calculate energy transferred to a known mass of water based on temperature change.

c in the equation Eh = c mΔT

Specific heat capacity of water, which is 4.18 kJKg-1°C-1.

ΔT in the equation Eh = c mΔT

The temperature change measured in degrees Celsius.

Calculation of moles (n)

n = m / GFM, where m is mass in grams and GFM is the gram formula mass.

Exothermic reaction

A reaction that releases heat, indicated by a negative enthalpy change (ΔH).

Common mistake when calculating Eh

Using the mass of the substance instead of the mass of water.

Units of Eh and ΔH

Eh is measured in kJ, while ΔH is measured in kJmol-1.

Energy lost to surroundings

A reason for inaccuracy in combustion experiments due to heat dissipation.

Causes of experimental error

Incomplete combustion, evaporation of the fuel, and uneven temperature distribution.

Thermodynamics principle of enthalpy

Enthalpy changes help understand energy changes in chemical reactions.

Heat shield

A method used to minimize heat loss to the surroundings during experiments.

GFM of methanol (CH3OH)

32 g.

GFM of ethanol (C2H5OH)

46 g.

The combustion of ethanol reaction

C2H5OH + 3O2 🡪 2CO2 + 3H2O.

ΔH calculation from Eh and n

ΔH = Eh / n, where n is the number of moles of substance used.