Chemistry111chapter5

Is transferred from surroundings to the system system

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Unformatted text preview: m surroundings to the system system Energy Units Energy The units for energy – Joule (J) – SI unit for thermal energy 1 J = 1 kg*m2/s2 Joule is small so it will be in kJ most of the time Energy Units Energy calorie (cal) – heat required to raise the calorie temperature of 1.00 g of pure liquid water from 14.5 to 15.5oC from 4.184 joule (J)= 1 calorie (cal) dietary Calorie (Cal) = 1000 cal Specific Heat Capacity Specific Heat transfer depends on Heat 1. 1. 2. 3. Quantity of material Size of the temperature change Identity of the material gaining or losing heat Specific heat capacity (C), or specific heat, is Specific the quantity of heat required to raise the temperature of 1 gram of a substance by 1 K temperature – – – Units are J/(g*K) q=C x m x ∆T ∆T = Tfinal - Tinitial q=C Heat transferred=specific heat x mass x change in Heat Temperature Temperature Specific Heat Specific Copper has a specific heat of 0.385 J/(g*K) Calculate the heat gained by a 10.0 g sample of Calculate copper if its temperature is raised from 298 K to 598 K. 598 q=(0.385 J/(g*K))(10.0 g)(598K-298K) = 1160 J If ∆T is +, q is +, endothermic If ∆T is -, q is -, exothermic Quantitative Aspects of Heat Transfer Transfer The specific heat capacity is a property of The a pure substance like density and boiling point point Measure specific heat by measuring Measure temperature changes that occur when heat is transferred to water heat Example Example 55 g piece of metal heated in boiling water 55 to 99.8oC and dropped into water in an to and insulated beaker insulated – Beaker has 225 g H2O and temp = 21.0oC – Final temp of water and metal 23.1oC – What is the specific heat capacity of the metal Water and metal end up at the same temp No heat is transferred to beaker or surroundings Heat transferred to metal so qmetal is neg. qwater = -qmetal -q water Energy and Changes of State Energy Change of state – a change between a Change solid, liquid, and gas solid, – Must apply energy to go from a solid to liquid Must and liquid to gas and Heat of fusion – heat required to convert a Heat solid to a liquid at its melting point solid Heat of vaporization – heat required to Heat convert a liquid to a gas at its boiling point convert Energy and Changes of State Energy When water changes from a solid to a liquid and When a liquid to a gas liquid – Temperature increases to 0oC and then stays and constant constant – Once the ice has melted, the temperature increases Once to 100oC and then stays constant to – When liquid water becomes a gas, the temperature When increases again increases TEMPERATURE IS CONSTANT TEMPERATURE THROUGHOUT A CHANGE OF STATE THROUGHOUT Enthalpy Enthalpy The heat content of a substance at The constant pressure is called the enthalpy, H constant – ∆H = change in enthalpy and we measure ∆H change in a reaction, not H in – Heat transferred at constant pressure can be Heat symbolized as qp symbolized Heat transfer at constant pressure is...
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