Thermal Energy and Matter Chapter 16

Heat Heat is the transfer of thermal energy from one object to another due to a temperature difference – Flows from hot object to cold object – Flow is spontaneous

Temperature – Temperature is the measure of kinetic energy of the particles in an object (atoms) due to their random motions through space – Particles transfer heat through collisions with other particles High energy lose energy as heat Lose energy gain energy as heat Temperature scales – Farenheit – Celsius – Kelvin

Thermal Energy Thermal energy is the total potential and kinetic energy of all the particles in an object Thermal energy depends on the mass, temperature, and phase (solid, liwuid, or gas) of an object

Thermal Contraction and Expansion Thermal expansion is an increase in the volume of a material due to a temperature increase – Particles move further apart as temperature increases

Specific Heat Specific heat is the amount of heat needed to raise 1 gram of material by 1 °C The lower the specific heat of a material the quicker it will increase in temperature when heated.

Specific Heat Q = heat (joules) m = mass (grams) c = specific heat (J/g·°C) ΔT = change in Temperature (°C)

Problem An iron skillet has a mass of grams. The specific heat of iron is J/g°C. How much heat must be absorbed to raise the skillet’s temperature by 95.0°C?

Problem How much heat is needed to raise the temperature of g of water by 85.0°C?

Problem How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C?

Problem In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water’s temperature? (Hint: Rearrange the specific heat formula to solve for ∆T.)

Problem To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of the silver increase?

Problem What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it?

Thermodynamics Conduction is the transfer of thermal energy with no transfer of matter The further the particles are away from another, the slower the transfer of heat – Gasses (slowest) – Liquids – Solids (fastest)

Thermodynamics Conductors – A material that conducts thermal energy well Insulators – A material that conducts thermal energy poorly

Thermodynamics Convection – The transfer of thermal energy when particles of a fluid (liquid or gas) move from one place to another Convection current – When a fluid circulates in a loop as it alternately heats up and cools down Hot air rises and cold air sinks

Thermodynamics Radiation – The transfer of energy by waves moving through space – All objects radiate energy – As an object’s temperature increases, the rate at which it radiates energy increases

Thermodynamics Thermodynamics is the study of conversions between thermal energy and other forms of energy First law of Thermodynamics Energy is conserved – energy cannot be created or destroyed, but converted into different forms Second Law of Thermodynamics Thermal energy can flow from colder objects to hotter objects only if work is done on the system Third Law of Thermodynamics Absolute zero cannot be reached

Heat Engines External Heat Engine – An engine that burns fuel outside the engine – Ex. A steam engine Internal Combustion Engine – An engine that burns fuel inside the engine – Ex. Car engine