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HEAT- Chapter 9 Temperature and Thermal Equilibrium The temperature of an object is proportional to the average kinetic energy of particles in a substance The energy associated with atomic motion is internal energy(U). When energy is added to a substance, its average kinetic energy, and thus its temperature increases Thermal equilibrium Thermal equilibrium is reached when the thermal energy of 2 substances is the same. Thermal energy moves from hot to cold. If a can of soda is placed in the freezer, the thermal energy of the soda will transfer away from the can to the outside air in the freezer. This will continue until the can and its contents reach thermal equilibrium. Increasing the temperature of a gas at constant pressure causes the volume of the gas to increase. Thermal expansion is the tendency of a substance, when heated, to increase in volume. In general, the volume of a liquid will decrease as temperature decreases; the exception is water Solids tend to have the smallest coefficient of volume Coefficient of Volume Expansion- a number assigned to different material to show the thermal expansion characteristic of the material Gases have highest coefficient; solids the lowest Measuring Temperature In a thermometer, the change in length of the liquid in the thermometer is proportional to the temperature change 3 scales used to measure temperature: Fahrenheit- used in United States Celsius- used by other countries and scientific community Kelvin-a scale used by scientists that measures absolute zero. Fahrenheit Scale: Freezing point of water: 32° Boiling point of water: 212 ° Celsius Scale Freezing point of water: 0 ° Boiling point of water: 100 ° Kelvin Scale: 0 = absolute zero Freezing point of water: 273K Boiling point of water: 373K Heat – thermal energy that is transferred. Unit- Joules (J) Heat’s symbol- Q Thermal Conduction: how heat is transferred Conduction- heat travels through touching atoms (solids) Convection- heat transfer in fluids Radiation-heat transfer over a distance; can take place through the vacuum of space Conservation of Energy- total energy is conserved ΔPE + ΔKE + ΔU= 0 The change in potential energy + the change in KE + the change in internal energy = 0 Changes in Temperature & Phase Specific Heat Capacity-the energy required to change the temperature of 1kg of a substance by 1° C Every substance has a unique Specific Heat capacity. Tells how much the temperature of a given mass of a substance will increase or decrease, depending on the how much energy is added or removed as heat C𝑝= Q/mΔT: Specific Heat Capacity=energy transferred as heat/mass x change in temperature Specific Heat Capacities Table Calorimeters- used to determine the specific heat of substances 𝑪𝒑𝒘 𝑴𝒘 ∆𝑻𝒘 = −𝑪𝒑𝒙 𝑴𝒙 ∆𝑻𝒙 w stands for water; Specific heat x Mass(kg) x change in Time= Released heat x Mass(kg) x change in time Phase Changes & Temperature Temperature increases until a phase change. During the phase change, temperature does not increase or decrease. After all of the substance has changed phase, temperature will increase (or decrease) until the next phase change. Latent Heat-the heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without change of temperature.