Energy

1. Energy energy- the capacity to do work or produce heat kinetic energy - energy of motion potential energy - energy of position

2. flow of energy HEAT Temperature average kinetic motion Thermal Equilibrium when objects reach a constant temperature Exothermic When heat (q) flows away from object or reaction Endothermic When heat (q) flows into an object or a reaction

3. Heat Transfer Specific heat capacity - the amount of energy needed to change the temperature of 1 g of substance by 1 oC (or K) substance specific heat cal/g.oC Al ---------------------- 0.22 Pb ----------------------- 0.038 Cu ---------------------- 0.092 Fe ---------------------- 0.11 ethanol(l) ------------- 0.59 CCl4(l) ----------------- 0.21 H2O(l) ----------------- 1.00 H2O(s) ----------------- 0.48

4. Example Problem heat transferred = (S.H.)(mass)(DT) Example: A lake that is 1 square mile and 10 feet deep contains 7.9 x 109 L of water. How many joules of energy must be transferred to the lake to raise the temperature by 1 oC? (densityH2O = 1.0g/mL) Mass of water = 1000 mL 1.0 g 7.9 x 109 L x x = 7.9 x 1012 g mL 1.0 L 1.0 cal Heat transferred = x 7.9 x 1012 g x (+1 oC) g.oC = 7.9 x 1012 cal

5. Heat Transfer Between Substances What is the final temperature of 323.4 g H2O initially at 21.7 oC, when 79.2 g of iron 71.9 oC are added? Specific Heat Capacity J/g.oC H2O 1.00 Fe 0.11 The fundamental principle here is that the energy lost by the substance initially at higher temperature is equal to the energy gained by the substance initially at lower temperature. -qhotobject = qcold object - qFe = qH2O -(S.H.Fe)(m)(Tf - Ti,Fe) = (S.H.H2O)(m)(Tf - Ti,H2O) -(0.11 cal/g.oC)(79.2 g)(Tf - 71.9 oC) = (1.0 cal/g.oC)(323.4 g)(Tf - 21.7 oC) Tf = 23.0 oC