Thermal Energy and Heat

What is heat? Heat is the transfer of thermal energy from one object to another because of a temperature change. Heat spontaneously changes from hot objects to cold objects. This happens due to a transfer of energy due to collisions. Low energy objects gain energy in collisions and high energy particles lose energy. Example: heating a frying pan-thermal energy transferred from the burner to the pan

What is temperature? Temperature is a measure of how hot or cold an object is compared to a reference point. On the Celsius scale, the reference points are the boiling points and freezing points of water. On the Kelvin scale, the reference point is absolute zero (0K) Temperature is related to the average kinetic energy of the particles in an object due to their random motions through space.

Thermal energy Thermal energy is the total potential and kinetic energy that make up on object Depends on mass, temperature, and phase (solid, liquid, or gas) of the object

Thermal expansion Thermal expansion is an increase in the volume of a material due to a temperature increase Thermal expansion occurs when particles of matter move farther apart as temperature increases. Gases expand more than liquids and solids

Specific heat Specific heat is the amount of energy needed to raise the temperature of one kilogram of a material one degree celsius. The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass. Specific heat is measured in joules per gram per degree celsius or J/gC

The heat (Q) absorbed by a material equals the product of the mass (M), the specific heat (c), and the change in temperature Q = m x c x T A calorimeter is an instrument used to measure changes in thermal energy. A calorimeter uses the principle that heat flows from a hotter object to a colder object until both reach the same temperature.

Heat and thermodynamics Conduction is the transfer of thermal energy with no overall transfer of matter. Occurs between two objects that touch Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often.

Heat and thermodynamics In metals conduction is faster because some electrons are free to move about and collide with one another and with atoms or ions transfer thermal energy A thermal conductor is a material that conducts thermal energy well example: wire oven rack A thermal insulator is a material that conducts thermal energy poorly example: air

Convection Convection is the transfer of thermal energy when particles of a fluid move from one place to another A convection current occurs when a fluid circulates in a loop as it alternately heats up and cools down. Convection currents are important in many natural cycles such as ocean currents, weather systems, and movements of hot rock in the earth’s interior

radiation Transfer of energy by waves moving through space All objects radiate energy. As an object’s temperature increases, the rate at which it radiated energy increases.

Thermodynamics Thermodynamics is the study of conversions between thermal energy and other forms of energy. The first law states that energy is conserved. The second law of thermodynamics states that thermal energy can flow from colder objects to hotter objects only if work is done on the system. The third law states that absolute zero cannot be reached (the lowest temperature possible -273 .15 degrees celsius)