Heat and Thermodynamics cheat sheet

Heat and Thermodynamics cheat sheet

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  RapidLearningCenter.com © RapidLearning Inc. All Rights Reserved AP Physics - Core Concept Cheat Sheet 13: Heat and Thermodynamics Key Physics Terms • Thermodynamics: The study of processes in which energy is transferred as work or heat. • Temperature: A measure of the average kinetic energy of the particles. The higher the temperature the faster the molecules move. • Linear Expansion: A change in length of a solid due to a temperature change. Proportional to the linear expansion coefficient,α, for the material. • Volume Expansion: A change in volume of a solid due to a temperature changes. Proportional to the volume expansion coefficient,β, for the material. Note β ≅ 3α • Energy: The ability to do work or supply heat. • System: The object or objects being studied. • Surroundings: Everything surrounding the system. • Internal Energy: The total energy of all the molecules in the system • Heat: The transfer of energy from one object to another due to a difference in temperature. • Work: In thermodynamics the work done by the system is positive; the work done on the system is negative. • Calorie: The amount of heat required to raise the temperature of 1g of water by 1°C. 1 calorie = 4.18 Joules. • State Function: Quantity which is dependent only on the current state of the system not the path taken to reach that state, e.g. Temperature. • Specific Heat Capacity: The amount of energy required to change a unit mass of a substance by 1°C. • Heat Capacity: The amount of heat needed to raise a mass of a substance, given by the product of mass and specific heat capacity. • Endothermic reaction: A reaction in which energy is absorbed into the system from the surroundings. • Exothermic reaction: A reaction in which energy is released from the system into the surroundings. • Calorimetry: A quantitative measurement of energy lost/gained from the system, which is equal & opposite to that lost/gained from the surroundings. • Latent Heat: The energy required to change the phase of a substance, without changing the temperature of the substance. • Heat of fusion: The heat required to change 1kg of a substance from a solid to a liquid state, which is equal to the heat lost when the liquid changes to a solid state. • Heat of vaporization: The heat required to change 1kg of a substance from a liquid to a vapor phase, which is equal to the heat lost when the vapor changes to a liquid phase. • Thermal Equilibrium: Two objects in thermal contact cease to exchange net energy. • Zeroth Law of Thermodynamics: If two systems are separately in thermal equilibrium with a third system. The first two systems are in thermal equilibrium with each other. • 1st Law of Thermodynamics (Law of Conservation of Energy): When heat flows into a system the energy must either appear as increased internal energy or work done by the system on its surroundings. • Entropy: A quantitative measure of the disorder of a system. • 2nd Law of Thermodynamics: The total entropy of the universe can never decrease. Natural processes tend towards disorder, greater entropy. • Heat Engine: A device that converts thermal energy into mechanical work. • Ideal Heat Engine: An engine with an efficiency of 1. • Efficiency: The ratio of the work done by the heat engine to the heat input to the engine. Variables Used and Their Metric Units • T = Temperature, °C, K • α = Linear expansion coefficient, (°C)-1 • β = Volume expansion coefficient, (C°)-1 • L = Length, m • V = Volume,m3 • U = Internal energy, J • Q = Heat, J • W = Work, J • Cp: = Specific heat , J/kg•°C • m = Mass, kg • C = Heat capacity, J/°C • Lfus= Heat of Fusion, kJ/kg • Lvap= Heat of Vaporization, kJ/kg • S = Entropy, J/kg • ε = Efficiency Key Formulas • ΔL = L x α x ΔT • ΔV = V x β x ΔT • β ≅ 3α • Q = Cp m x ΔT or Q = C x ΔT where C = Cp m • ΔQfus = m x Lfus • ΔQvap = m x Lvap • U = Q – W • ΔStot ≥ 0 • ΔSsys + ΔSsur ≥ 0 • out in W ε = Q 1st Law of Thermodynamics 1st Law of Thermodynamics When heat flows into a system the energy must either appear as increased internal energy or work done by the system on its surroundings. This is a statement of the conservation of energy. U = Q – W Q is the heat added to the system. W is positive when work is done by the system on its surroundings: U = Q – W W is negative when work is done on the system, by surroundings: U = Q – (-W) = Q + W Special cases of the 1st Law Adiabatic: No heat transfer, Q = 0, ∆U = -W=-PΔV Constant-volume: No work is done, W = 0, ∆U = Q Cyclical: No change in internal energy, ∆U = 0, Q = -W Free expansion processes: Irreversible, ∆U = Q = W 2nd Law of Thermodynamics Entropy is a measure of disorder. If the entropy of the system decreases during a reaction, the entropy of the surroundings increases by an equal or greater amount. Statements of the 2nd Law of Thermodynamics: 1) The total entropy of the universe can never decrease, only increase or remain the same. ΔS ≥ 0. 2) Heat flows from a hot object to a cold object but never the reverse. 3) There cannot be a 100% efficient heat engine; one that changes a given amount of heat entirely into work: out in W ε = 1 Q < How to Use This Cheat Sheet: These are the keys related this topic. Try to read through it carefully twice then write it out on a blank sheet of paper. Review it again before the exams.