Required Practical 2 - Enthalpy Change

State the equation for energy change.

Q = m x SHC x change in T

What is calorimetry?

An experiment where substances are mixed in an insulated container and the temperature change is measured

Describe the method for a calorimetric experiment.

1. Wash the apparatus with appropriate solutions

2. Put the polystyrene cup into a beaker for insulation and support

3. Measure the volumes of the first solution using a pipette and add to the cup

4. Place the thermometer in the cup 

5. Measure the initial temperature of the solution every minute for 2 minutes

6. At the third minute, add the second solution to the cup, stir and close the lid

7. Measure the temperature every minute for 15 minutes 

How is the graph used to determine the temperature change of the solution?

Extrapolate the cooling curve back to the time when the reactants were mixed together

State some common errors in the experiment.

Heat loss to the surroundings

Incomplete or slow reactions

Approximation of the SHC of the solution

Describe how to calculate the enthalpy change from results. 

1. Use the calculation to find q

2. Calculate the number of moles of each substance used

3. Divide q by the initial number of moles of the limiting reactant

4. Add signs and units

What is flame calorimetry?

An experiment to determine enthalpy change by burning a mass of fuel to heat a known mass of substance 

What 3 things need to be measured in a flame calorimetry experiment?

The mass of fuel before and after

The temperature change of the water 

The mass of water heated 

Describe a detailed method to measure the enthalpy change of a solution of anhydrous copper (II) sulphate.

1. Weigh out approximately 4g of anhydrous copper sulphate in a weighing boat and record the mass

2. Using a volumetric pipette, place 25cm³ of distilled water into a polystyrene cup and record the initial temperature

3. Start the timer and record the temperature every minute, stirring continuously

4. At minute 4, add the copper sulphate and stir don’t record temp.)

5. Record the temperature of the solution every minute for 15 minutes

How can the measurement of the enthalpy change of anhydrous copper sulfate be used to calculate the enthalpy change when forming a hydrated salt?

Measure the enthalpy change of hydrated copper sulfate and use Hess’s law