Chapter 11 Heat

Chapter 11 Objectives Define heat Identify specific heat Differentiate between types of latent heat Identify types of heat transfer Account for insulation

Heat Recall that heat is defined as the amount of energy that is transferred between a system and its environment. A common unit of measurement for heat is the calorie (cal). –The heat required to raise one gram of water 1 o C A related unit is the kilocalorie, or 1000 calories. –The Calorie (with a capital C) is equivalent to 1 kilocalorie. This is the Calorie that you hear of when talking of food. Another common unit of measurement for heat is the British Thermal Unit (BTU). –The heat required to raise 1 lb of water 1 o F Common unit of heat rating for furnaces and other appliances The SI base unit for heat is the same as energy –Joule (J)

Specific Heat The specific heat of a substance is defined as the amount of heat requires to raise 1 kg of it by 1 o C. This varies for different materials. Can be measured in J/kg o C or cal/g o C Q = mc  T Heat Specific Heat Tempertaure ( o C)

Phase Change While an object is transferring heat without changing phase, then you must use the equation involving specific heat. An object will also transfer heat and change phase. This is called latent heat. –Also known as hidden heat because this occurs where there is no temperature change. Units are J / kg There are two types of latent heat – Heat of Fusion – Heat of Vaporization

Fusion vs Vaporization Heat of Fusion is the heat transferred during a phase change between solid and liquid. Denoted by L f Heat of Vaporization is the heat transferred during a phase change between liquid and gas. Denoted by L v Q = mL Latent Heat

Heating Curve for H 2 O solid liquid gas heat of fusion heat of vaporization use specific heat while substance remains in same phase Q = mc  T use latent heat while substance changes phase Q = mL

Types of Heat Transfer There are three types of heat transfer –Remember heat is not transferred between a system and its surroundings when they are at the same temperature. Conduction –Heat transferred as a result of direct contact. Convection –Heat transferred as a result of the movement of a heated substance past another substance. Radiation –Heat transferred as a result of energy given off from a substance without contact or movement of any molecules.

Conduction An example of conduction would be ice cubes in a glass of water. We can classify the rate at which that heat is conducted called the heat transfer rate, H. –Often called a heat current. Q tt H =

Convection Convection can occur in two ways –Natural convection Movement of molecules as a result in different densities of the substances. –Ex: Hot air rises –Force convection When the heated substance is forced to move by a fan or pump. –Ex: Furnace systems

Radiation Radiation is the heat felt by placing your hands next to a fire. –On top of the fire would be convection! Example of this would be how the sun heats the Earth. –Also what you experience by cooking in a microwave.