1. Topic B Work, Calorimetry, and Conservation of Energy

2. Energy can also be transferred via work.
In chemistry, we think of work in terms of gases and their expansion and contraction.
Consider a gas inside a piston.

3. particles collide with the piston
As the gas expands:
particles collide with the piston
energy is transferred from the gas to the piston
Work is done by the gas on the piston
expressed as w = PΔV [ Work = F  d ]
- it does work on the piston
- energy is transferred to the piston
- the piston moves.
Because of conservation of energy,
any energy lost by one system (in this case the gas),
must be gained in equal magnitude by the other system (in this case the piston)
In this work scenario, energy flows from one system to the other.

4. Heating and cooling curves:
Indicate graphically changes from one phase to another as energy is added or removed
Only the temperature is changed and heating and cooling curves result.
Starting with a solid below its melting point the following effects can be observed.

5. 1. The temperature of the solid increases at a constant rate until it begins to melt.
2. When melting begins, the temperature is constant until the solid has all turned to liquid.
3. The temperature of the liquid increases at a constant rate until it begins to boil.
4. When boiling begins, the temperature is constant until the liquid has all turned to gas.
5. The temperature of the gas increases at a constant rate.

6. In summary:
Energy is either being used to change the temperature but not the phase,
Or it is being used to change the phase and not the temperature.
A plateau represents a stage when two phases are in equilibrium with one another and the phase change is occurring.

9. The heat capacity of the water must be known.
Calorimetry :
Calorimetry is a technique used to measure energy changes in a chemical system.
In chemistry, calorimetry measures energy change in a chemical reaction
Typically water is used to measure heat released by the reaction (+ΔT of water)
Or heat being absorbed by the reaction (-ΔT)
The heat capacity of the water must be known.

10. The chemical reaction takes place, and energy is transferred between the chemical reaction and the water.
If we know the specific heat capacity of the water (a.k.a. the heat bath), then we can calculate the amount of energy that has been lost or gained by the water
q = m c ΔT
If the temperature of the water increases – chemical reaction released energy (exothermic).
If the temperature of the water goes down - chemical reaction absorbed energy (endothermic).

11. We assume that the energy lost or gained by the chemical reaction is equal to the energy gained or lost by the heat bath.
Heat Lost = Heat Gained

12. Practice:
(1)
Propane is commonly used in gas grills. A sample of propane with a mass of 44.0 g, is completely burned in oxygen and in the process it releases 2002 kJ of energy. A transfer of energy from the reaction to the water takes place.
Assuming the specific heat capacity of water to be J g-1 K-1, and that in 100 % of the energy generated is transferred to the wate,r answer the questions that follow.
(a) In which direction does the energy flow?
(b) Calculate the change in temperature of kg of water.
(c) Is the combustion (burning) of propane an exothermic or an endothermic process? Explain your answer.

13. (2) Consider the following:
(a) How much energy is released, when 1.00 mole (18.0 g) of water at 20.0 oC is frozen, and then cooled to a temperature of oC?
(b) Considering ONLY the energy released in the phase change above, what would be the temperature rise observed in a heat bath made of gold, that has a specific heat capacity of J/gK and a mass of kg?
Specific Heat of Ice
2.05 J/gK
Specific Heat of Water
4.18 J/gK
Specific Heat of Steam
2.08 J/gK
Molar Heat of Fusion for H2O
6.02 J/mol
Molar Heat of Vaporization for H2O
40.7 kJ/mol
Melting Point of Ice
0.00oC
Boiling Point of Water
373 K