1. Module 3 Lesson 4 – Calorimetry and enthalpy change of combustion

2. Objectives Must Follow a set of instructions to set up practical equipment safely and quickly Should Use the equipment provided to investigate the heat given out when a substance burns Could Calulate a value for ΔH c.

3. Equation for ΔHc Balance the following equations for burning methanol and ethanol in air and add the correct state symbols for the substances in their standard states: __CH 3 OH + __O 2  __CO 2 + __H 2 O __C 2 H 5 OH + __O 2  __CO 2 + __H 2 O In an equation to represent ΔHc you must not put a balancing number in front of the substance being burnt. If you do, then more than 1 mol would have been combusted. AfL – what are standard conditions?

4. The correct equations CH 3 OH(l) + 1½O 2 (g)  CO 2 (g) + 2H 2 O(l) C 2 H 5 OH(l) + 3O 2 (g)  2CO 2 (g) + 3H 2 O(l)

5. Calorimetry

6. How does calorimetry work? A known volume of cold water is measured into the beaker/can The starting temperature of the water is recorded The water is heated using the flame from the burning fuel The final temperature of the water is recorded The spirit burner containing the fuel is weighed before and after the experiment.

7. Practical Follow the instructions on Activity sheet 26 to compare the enthalpy of combustion of methanol and ethanol.

8. Calculations

10. Energy per gram of fuel

11. Errors The figure you have calculated is lower than the figure found using bond energies (remember breaking and making bonds). Why do you think this could be?

12. Errors Why do experimental values for ΔHc deviate from their theoretical counterparts. Energy lost to the surroundings Incomplete combustion Conditions which are not standard (ie not 298K and 1atm pressure)

13. Examination questions (AS)

16. Mark scheme

17. Examination question

20. Mark scheme

21. Homework Complete the practical write up and examination paper questions. Short test next lesson on enthalpy changes – learn your definitions. YOU MUST DO THIS OR YOU WILL NOT UNDERSTAND THE NEXT BIT!