Aim: What is thermochemistry? Do Now: For each blank select the correct word. When your hands are cold you put them by the heater. Based on this experience, heat transfers from _______________ to ________________. Therefore, heat transfer from ______________ ; (heater/hands) (heater/hands) (warmer/cooler) objects to ________________ objects. (warmer/cooler)
Law of Conservation of Energy In any chemical or physical process, energy is neither created nor destroyed. There are different forms of energy and energy can be changed from one form to another. Chemical energy Electrical energy Electromagnetic radiation Heat (thermal) energy Mechanical energy Nuclear energy
Heat Heat q is energy that transfers from one object to another because of a temperature difference between them.
Heat Flow Heat always flows from a warmer object to a cooler object until the temperature of both objects is the same.
Exothermic and Endothermic Process Exothermic process: Energy is GIVEN OFF in a chemical reaction from the system to the surroundings. System become cooler Endothermic process: Energy is ABSORBED in a chemical reaction by the system from the surroundings System becomes hotter
How do we measure energy? Energy is measured in units of calories or joules. 1 Calorie = 1 kilocalorie = 1000 calories 1000 joules = 1 kilojoule 1 J = 0.2390 cal 4.18 J = 1 cal
Heat Formula (how much heat in joules is absorbed or released) – Table T q = mCΔT q = heat m = mass C = specific heat capacity ΔT = change in temperature ( T final – T initial) * If the reaction is endothermic (energy is absorbed) q will be a positive number. If the reaction is exothermic (energy is released) q will be a negative number.
Specific Heat Capacity Specific heat capacity of a substance is the amount of heat it takes to raise the temperature of 1g of the substance 1oC. Specific heat of water = 4.18 J/g •C (Table B) 4.18 joules is needed to raise 1 gram of water 1oC
Problem 1 How many kilojoules of heat are absorbed when 1000 g of water is heated from 18oC to 85oC?
Problem 2 The temperature of a 95.4 g- piece of copper increases from 25oC to 48oC when copper absorbs 849 J of heat. What is the specific heat of copper?
Practice 1. How much heat is absorbed when 500. g of water , C = 4.184 J/g•C, goes from 25.0oC to 35.0oC? 2. How much heat is absorbed when 500. g of copper, C = 0.385 J/g•C , goes from 25.0oC to 35.0 oC? 3. How much heat is released when 150. g of iron cools from 525oC to 100OC? (C = 0.44 J/g•C) 4. A 50.0 g block of glass (C = 0.50 J/g•C) absorbs 333 joules of heat energy. How much does the temperature of the glass rise?
Practice 5. The temperature of a silver coin (C= 0.24 J/g•C) falls by 353oC as it releases 5,550 Joules of heat. What is the mass of the coin? 6. An aluminum can with a mass of 12.5 grams (C = .90 J/g•C) absorbs 245 Joules of heat. How much does the temperature rise?