1. Enthalpy Starter: BACK OF BOOK:
Why does a mixture of propane and oxygen not explode as soon as it is mixed?

2. Endothermic and Exothermic reactions
understand that chemical reactions in which heat energy is given out are described as exothermic and those in which heat energy is taken in are endothermic describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation in which heat energy changes can be calculated from measured temperature changes calculate molar enthalpy change from heat energy change understand the use of ΔH to represent enthalpy change for exothermic and endothermic reactions

3. Key words Exothermic reaction 발열반응 Rate of reaction 반응 속도
Endothermic reaction 흡열반응
Collision 충돌사고, 부딪침

4. Activation Energy
Activation energy is the energy needed to break the bonds between the atoms in the starting materials so they can react. Breaking bonds takes energy (is endothermic).
The lower the activation energy, the easier it is to start the reaction.
e.g. It is easier to make nitrogen tri-iodide react than burn wood.

5. Energy cannot be created or destroyed
Thermodynamics:
All energy leaves a system is transferred to the surroundings & vice versa
The first law of thermodynamics states:
Energy cannot be created or destroyed
The energy that is transferred to the surroundings is not lost – its is spread through the surroundings

6. Energy Level Diagrams:
Exothermic Reactions:
Enthalpy of reaction (Energy Change) is negative
The energy content of the system has decreased
Some energy has left the system & entered the surroundings as heat
Hproducts < Hreactants
*There is a net
decrease in the potential energy of
the system
ΔH is negative

7. Exothermic Reactions
Exothermic Reactions overall release heat energy – they lead to rises in temperature.
e.g. Burning Wood
Reactants
Energy Released
Energy
Products
Progress of the reaction

8. Hproducts > Hreactants
Endothermic Reactions:
the enthalpy of reaction is positive
Energy content of the system has increased as it has gained from the surroundings
Hproducts > Hreactants
So ΔH is positive
Energy is transferred from the surroundings
There is a net increase in the potential energy of the system

9. Endothermic Reactions
Endothermic Reactions overall take in heat energy – they lead to a lowering of the temperature.
e.g. the reaction used in sports cold packs
Products
Energy Absorbed
Energy
Reactants
Progress of the reaction

10. Practice: Mini whiteboards
Draw enthalpy level diagrams for:
The endothermic reaction:
H2O (g) + C (s)  H2 (g) + CO (g)
b. The combustion of methane:
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (l)

11. Endo - Exo Thermic Method
1. There will be 5 stations around the room and you have 5 experiments to complete.
2. You will be using boiling tubes. Wash out after each experiment.
3. Take 20cm3 of the solution and measure the temperature using a thermometer.
(One station has 2 solutions measure either one).
(One station has 2 solids dissolve the Citric acid in 20cm3 of water).
4. Add the second chemical. Either 20cm3 of solution or 2 spatulas of a solid.
(Only 1 piece of Magnesium).
5. Measure the temperature change after and calculate the temperature change.
6. Rinse out your cup and lid and move on to the next station.

13. Plenary Check point:
Classify each process as endothermic or exothermic:
The burning of magnesium in air
The crystallisation of copper (II) sulfate from a saturated solution
The thermal decomposition of magnesium nitrate
The fermentation of glucose by yeast
The evaporation of sea water
The combustion of magnesium
Exo
Exo
Endo
Exo
Endo
Exo