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2303_-_Spr_2010_-_Week_2_-_Heat

# 2303_-_Spr_2010_-_Week_2_-_Heat - Week 2 1 Heat Homework...

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Week 2 - 1 Heat Homework Review Reversible and irreversible processes Heat Reading: 18.2 – 18.3 Lecture notes will be posted each week Popping corn is an example of an irreversible process serc.carleton.edu

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Thermodynamics We will study thermodynamics to understand engines. 22 Watt steam engine, Wikipedia
Thermodynamic Reversibility Change 1 thermodynamic variable, and bring it back. Reversible process: System is always in thermal equilibrium Irreversible process: System is not always in thermal equilibrium Examples of irreversible processes: Free expansion of gases Melting of ice in hot water Frictional heating 33 gallery.hd.or g

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Reversible and Irreversible Processes When we talk about a reversible process, we mean it is slow enough that gas remains in thermal equilibrium. Piston moved very slowly- reversible Membrane breaks- irreversible
Reversible Process When piston is moved slowly, the system remains in thermal equilibrium with the reservoir, and the process is reversible. 55

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Example of an Irreversible Process The gas expands freely when the valve is opened wide. 66
Heat Heat is a mechanism by which energy is transferred between a system and its environment or from one system to another due to a temperature difference. 77 The term heat will also be used to represent the amount of energy, Q, transferred by this mechanism.

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18-2 Heat Flow The temperature of a system is related to its internal (thermal) energy. The system can transfer energy by changing the temperature or phase of another system, by doing work, or both. When the temperature of the system changes, there has been heat flow Q , or work done . 88
Week 2 – 2 Heat Flow Agenda Heat Capacity Latent Heat Thermal Conduction Thermal Resistance Reading: Chapter 18 Homework #2 on WebAssign 99 Typical heat loss for a house in winter. pinkbatts

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Heat Capacity The heat capacity C determines how much heat is needed to raise the temperature of an object by 1 E C. 10 10 1 cal of heat will raise 1 g of water 1 °C. C cal C water ° = / 1 capacity Heat Watch units 1 food calorie = 1 kcal K g cal c water = / 1 heat Specific
11 Add Energy to System What can happen when we add energy to a system? 1. Raise temperature Ø Will Al or H2O heat faster? 1. Phase change 1. System could do work or transfer heat to another (cooler) object (transfer energy out)

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12 Typical Specific Heat Substance J/kg/K cal/g/K Water 4180 1.00 Alcohol 2540 0.61 Ice 2090 0.50 Steam 2010 0.48 Air (50 oC) 1050 0.25 Aluminum 900 0.22 Glass 840 0.20 Steel 450 0.11 Specific Heat Capacities Table R. Vawter
Latent Heat A phase change occurs when: Solid melts to liquid Liquid boils to gas Gas condenses to liquid Liquid freezes to solid. Each of these phase changes requires heat, although the temperature does not change.

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