Enthalpy – Continued

Δ H = Mass of Water x Specific heat capacity x θ of water

E.g.

0.21 g of Ethanol was used to heat 100 g of water.

The water’s temperature increased by 10 Celsius.

Δ H = Mass of Water x Specific heat capacity x θ of water

Δ H = 100 x 4.18 x 10

Δ H = 4.18 Kilo Joules

We can use this method to find out the enthalpy in a mole of the substance:

E.g. Knowing that 0.31 g of Ethanol gave 4.18 Kilo Joules of energy:

We divide by the mass and multiply by the molecular mass of the substance.

Δ H = 4.18 Kilo Joules ÷ 0.31 × 46

Δ H = 620.26 Kilo Joules

n.b. Don’t forget to use BASE UNITS before doing any calculation.