Chapter 9: Heat

Section 9.1: Temperature and Thermal Equilibrium

Defining Temperature Temperature: a measure of the average kinetic energy of the particles in a substance Adding or removing energy usually changes temperature

Internal Energy: energies associated with atomic motion Thermal Equilibrium: the state in which two bodies in physical contact with each other have identical temperatures Increasing the temperature of a gas at constant pressure causes the volume of the gas to increase (thermal expansion)

Measuring Temperature Thermometer a device that measures temperature. Mercury Alcohol Metal coils Digital

Measuring Temperature Calibrating thermometers requires fixed temperatures.

Measuring Temperature Celsius-Fahrenheit Temperature Conversion Celsius-Kelvin Temperature Conversion

Example Problem Oxygen condenses into a liquid at approximately at 90.2 K. To what temperature does this correspond on both the Celsius and Fahrenheit temperature scales?

Section 9.2: Defining Heat

Heat and Energy Heat: energy transferred between objects because of a difference in their temperatures. Energy is transferred as heat from objects with higher temperatures to those with lower temperatures. The greater the temperature difference is between objects, the greater the rate of energy transfer between them as heat.

Units of Heat Heat is measured in units of joules(J) 1 calorie (cal) = 4.186 J 1 kilocalories(kcal) = 4186 J 1 Calorie = 1kcal = 4186 J 1 British thermal unit = 1055 J 1 therm = 1.055 X 10⁸ J

Thermal Conduction Thermal conduction is the transfer of energy from differences in temperature. Energy between particles as they collide within a substance or between two objects in contact. The rate of thermal conduction depends on the substance. Substances that rapidly transfer energy as heat are called thermal conductors. Substances that slowly transfer energy as heat are called thermal insulators.

Convection and radiation also transfer energy. Convection involves the movement of cold and hot matter. Electromagnetic radiation is when objects reduce their internal energy by giving off electromagnetic radiation of particular wavelengths or are heated by electromagnetic radiation.

Heat and Work The sum of the changes in potential, kinetic, and internal energy is equal to zero. Conservation of Energy PE + KE + U = 0 If changes in internal energy are taken into account, the total energy is conserved.

Sample Problem ΔPE + ΔKE + ΔU = 0 What is the change in internal energy when the change in potential energy is 20 J and the change in kinetic energy is 35 J? ΔPE + ΔKE + ΔU = 0 20 J + 35 J + ΔU = 0 ΔU = -55 J Given: ΔPE = 20 J ΔKE = 35 J Unknown: ΔU = ?

Section 9.3: Changes in Temperature and Phase

Specific Heat Capacity Specific Heat Capacity: the energy required to change the temperature of 1 kg of a substance by 1°C Q = energy transferred as heat (J) m = mass of substance (kg) C = specific heat capacity ΔT = temperature change ( K or C)

Calorimetry: method used to determine specific heat capacity The energy absorbed by one substance is equal to the energy lost by another. Qlost = Qgained

Example Problem What is the final temperature when a 3.0 kg gold bar at 99°C is dropped into 0.22 kg of water at 25°C? (Cp x m x ΔT)water = (Cp x m x ΔT) gold (4186J/kg°C)(0.22kg)(Tf - 25°C) = (129J/Kg°C)(3.0k g)(99°C- Tf) 921Tf – 23,023 = 38,313 – 387Tf 1308 Tf = 61,336 Tf =47 ° C

Phase Change & Latent Heat Phase Change: physical change of a substance from one state to another at constant temperature and pressure When substances melt, freeze, boil, condense, or sublime, the energy added or removed changes the internal energy without changing the temperature.

Latent Heat: energy per unit mass that is transferred during a phase change of a substance Formula of latent heat: Latent heat is measured in the units . Lf = Heat of fusion, the latent heat of a substance that is melting. Lv = Heat of vaporization, the latent heat of a substance that is vaporizing.