REQURE PRACTICAL 2: measurement of an enthalpy change

Describe the experiment to measure an Enthalpy change

• wash equipment with solution used

• Dry cup after washing and put polystyrene cup in beaker for insulation and support

• Measure out desired volumes with pipette and transfer to insulated cup

• Clap thermometer immersed in solution

• Measure initial temp every 3 minutes

• Transfer reagent to cup and stir to ensure solution at the same temp

• Record temperature every minute after addition

Describe the flame calorimetry experiment for Enthalpy of combustion

• measure mass of spirit burner before and after

• Measure temperature change of the water and volume of water in the cup

How to get a better average temperature?

• take the temperature of reactants before they are added together

How to get the exact temperature rise

• take reading at regular time intervals

• Extrapolate curve back to when reactants are added together

What are some errors?

• energy transfer to surroundings

• Density of solution taken to be the same as water

• Assumes all water has the same specific heat capacity

What are the efforts for flame calorimetry?

• incomplete combustion

• Energy lost from calorimeter

• Evaporation of fuel After weighing

Why is it not easy to measure the temperature change for a solid?

• impossible to add the exact amount of water without the solid dissolving