Exothermic reaction

Endothermic reaction

Heat of precipitation

In an experiment to determine the heat of precipitation of silver nitrate,

50 cm³ of 1.0 mol dm^-3 hydrochloric acid is added to 50 cm³ of 1.0 mol dm^-3 silver nitrate solution.

The following results are obtained.

Initial temperature of silver nitrate solution (oC)	28.0
Initial temperature of hydrochloric acid solution (oC)	29.0
Highest temperature of the mixture (oC)	35.5

Calculate the heat of precipitation of silver chloride, AgCl

[Specific heat capacity of water is 4.2 J g^{-1 o}C^-1 and density of water is 1 g cm^-3]

(ans: - 58.8 kJ mol^-1)

Heat of precipitation (Find the heat change)

Calculate the heat change when 200 cm³ of 0.5 mol dm^-3 calcium chloride, CaCl₂  solution  is added to 200 cm³ of 0.5 mol dm^-3 sodium carbonate, Na₂CO₃ solution if the heat of precipitation of calcium carbonate, CaCO₃ is  +12.6 kJ mol^-1

[ Specific heat capacity of solution : 4.2 J g^{-1 0}C^-1 . Density of solution : 1 g cm^-3 ]

(ans: 1.26 kJ)

Heat of displacement (Experiment)

Heat of displacement (Calculation)

To determine the heat of displacement of copper from a copper (ll) sulphate solution by zinc.

Procedure :

1. Measure 25 cm³ 0.2 mol dm^-3 copper(ll) sulphate solution and pour into a polystyrene cup.

2. Put the thermometer into the copper(ll) sulphate solution. Record the initial temperature,

3. Add half a spatula of zinc powder (in excess) quickly into copper(ll) sulphate solution.

5. Stir the mixture with the thermometer and record the highest temperature achieved.

Result :

Initial temperature of copper(II) sulphate solution        =  30.0 ⁰C

Highest temperature of the mixture                              =  40.0 ⁰C

Calculate the heat of displacement of copper from a copper (ll) sulphate solution by zinc.

[ Specific heat capacity of solution : 4.2 J g^{-1 0}C^-1 . Density of solution : 1 g cm^-3 ]

(Ans: - 210 kJ mol^-1)

Heat of displacement (Find the change of temperature)

In an experiment, excess magnesium powder is added to 50 cm³ of 0.25 mol dm^-3 

iron(ll) sulphate solution. The thermochemical equation is shown below,

       Mg(s)   +   Fe²⁺ (aq)  à  Mg²⁺ (aq)  +   Fe (s)                  ΔH =  -80.6 kJ mol ^{- 1}  

What is the change in temperature?

[ Specific heat capacity of solution : 4.2 J g^{-1 0}C^-1 . Density of solution : 1 g cm^-3 ]

(ans: 4.8 ^oC)