1. ENERGY AND CHEMICAL CHANGE CH. 16 Energy is the ability to do work or produce heat and is found in two forms potential energy is energy due to the composition of the substance kinetic energy is the energy of motion (1/2 mv 2 )

2. Law of Conservation of Energy Law of conservation of energy: Energy can be converted from one form to another, but cannot be created nor destroyed

3. Energy and units Chemical potential energy often releases heat or needs heat Review- kinetic energy is the energy of motion Measuring in heat is done using units called Joules. One Joule is = 0.2390 calories One calorie = 4.184 Joules One Calorie = 1000 calories (note the capital C) = 1 kcal

4. Units and math Measuring in heat is done using units called Joules. One Joule is = 0.2390 calories One calorie = 4.184 Joules One Calorie = 1000 calories (note the capital C) = 1 kcal How many Joules are in a bowl of breakfast cereal and milk which contain 340 Calories?

5. Specific Heat Specific heat is the amount of energy required to raise the temperature of one gram of a substance one degree Celsius specific heat is measured in J/g o C specific varies based on the substance that is being measured water has one of the highest specific heats metals have lower specific heats (it heats up quickly)

6. Energy Diagram for Water 100 oC __D E C 0oC __ B -20 oC A Energy increase ____________________>>>

7. Key to energy diagram for water A = Ice heating ( 1 state of matter) S only B = Ice melting (2 states of matter – S and L C = Water heating ( 1 state of matter) L only D = Water boiling (2 states of matter) L and V E = Water vapor boiling (1 state of matter) V only Calculations for specific heat can only be used when the temperature changes (A, C, E)

8. Specific Heat To calculate heat absorbed or released by a substance: q = m c p  T q = heat absorbed or released (heat = temp) c p = the specific heat of the substance m = mass of the sample in grams  T = change in temperature in o C or T final - T initial

9. Specific Heat Math If the temperature of 34.4 g of ethanol has been raised from 25.0 o C to 78.8 o C how much heat has been absorbed by the ethanol? What if this sample were cooled from 78.8 o C to 25.0 o C?

10. Energy diagram for exothermic reaction  ctivation energy – Minimum amount of energy Reactants _ _ _ _ _ _ _ _ required to start the reaction  H is negative  H – The change in energy from reactants to products _ _ _ _ _ _ _ _ Products Time (increasing)

11. Energy Diagram of an endothermic reaction Activation energy +  H Reactants _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _products An endothermic reactions has a higher activation energy than an exothermic reaction  H is positive Energy increases

12. The effect of a catalyst on a chemical reaction A catalyst lowers the activation energy and shortens the path of a reaction A catalyst speeds the rate of reaction