Calorimetry (3.1.4.2)

How can heat change in a reaction be calculated?

q = mcΔT

Where q is heat change (J)

Where m is mass of substance (g)

Where c is specific heat capacity (Jg^-1K^-1)

Where ΔT is change in temperature (K)

Where m is the mass of the substance that has a temperature change ∆T and a specific heat capacity c.

How do you calculate molar enthalpy change of a reaction?

Δ_rH = q/n

Where Δ_rH is the enthalpy change of reaction (kJmol^-1)

Where q is heat change (J) - divide by 1000 to get to kJ

Where n is moles of reactant

How do you measure enthalpy change using calorimetry and what are the errors?

Method

1) Wash equipment with solution being used

2) Put a polystyrene cup in a beaker for insulation and support

3) Measure out desired volume(s) of solution(s) using volumetric pipettes and transfer to polystyrene cup

4) Place thermometer in cup and measure the initial temperature of the solution for 3 minutes

5) At minute 4 add desired mass (using balance (before and after weighing method)) of reagent to the cup

6) Stir mixture to ensure all the solution is at the same temperature

7) Record temperature of solution for several minutes after

Finding ΔT

1) Plot temperature against time using your results - skip minute 4

2) Draw two lines of best fit, one for the initial temperature, and the other following the cooling trend

3) Extrapolate both lines to the 4th minute

Finding Δ_rH

1) Use q = mcΔT - where m is the mass of the solution used and c is the solution’s specific heat capacity

2) Use Δ_rH = q/n - where n is the moles of the reagent added

Errors

1) Heat loss to the surroundings

2) Approximation in specific heat capacity of solution - assumes all solutions have the specific heat capacity of water

3) Reaction/dissolving may be incomplete/slow

4) Density of solution is taken to be the same as water

5) Some of the solution could’ve evaporated

6) If using fuel, incomplete combustion could’ve occured

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