Energy and Chemical Change

1. Energy and Chemical Change Ch 16 Part 1

2. Energy • The ability to do work or produce heat • Potential energy – energy due to composition or position of object • Kinetic energy – energy of motion • Law of conservation of energy • Energy can be converted from one form to another, but cannot be created or destroyed

3. Energy • Chemical potential energy • Energy stored in a substance because of its composition • Stored energy is converted to work (W) or heat (q) • Heat is measured in: • Calories (cal) – heat required to raise the temperature of pure water 1°C • Joules (J) • 1 cal = 4.184 J

4. Specific Heat • The amount of heat required to raise the temperature of one gram of the substance by 1°C • Substance with high specific heat take more energy to heat than substance with low specific heat • Specific heat of water – 4.184 J/(g·°C)

5. Calculating change in Heat q = c x m x ΔT q – work c – specific heat m – mass ΔT – change in temperature (°C)

6. Practice • If the temperature of 34.4g of ethanol increases from 25.0°C to 78.8°C, how much heat has been absorbed by the ethanol?

7. Changes of State • Phase changes absorb or release heat ΔHvap = molar enthalpy of vaporization • Heat required to vaporize one mole of a substance ΔHfus = molar enthalpy of fusion • Heat required to melt one mole of a substance

9. Practice • How many kJ of heat are required to melt 125 g of ice at its melting point?

10. Practice • A 44.7g sample of ice at -34°C is heated to steam at 138°C, how much energy is required?

11. Practice • How much energy is released from the combustion of 2 kg of octane?

12. Practice • How much energy is released from the combustion of 2 kg of ethanol?