What is HEAT? Heat is: A substance that flows from hot bodies to cold bodies (CALORIC HEAT). A form of energy that is transferred because of a temperature difference. UNITS: 1 calorie = energy to raise temperature of 1g of water from 12 to 13ºC 1 kilocalorie = 1000 cal = 1 Calorie 1 calorie = 4.18 Joules 1 BTU = 1 British Thermal Unit = 252 calories = 1055 Joules

TEMPERATURE, HEAT, INTERNAL ENERGY Temperature is a measure of the AVERAGE KINETIC ENERGY of molecules Heat is the energy transferred due to a temperature difference HEAT IS ON THE MOVE!! Internal energy is the sum of all the energy of the molecules of an object (including translational, rotational, and vibrational energy)

SPECIFIC HEAT Water has a high specific heat!!! To heat 1kg of water by 1ºC requires 4180 Joules (c = 4180 J/kg ºC) To heat 1kg of steel by 1ºC requires 450 Joules (c = 450 J/kg ºC) C = Q/mΔTORQ = mc ΔT

How can we heat things up?? You add thermal energy to an object by doing work on the object:

How can we heat things up?? You add thermal energy to an object by doing work on the object: If you rub an object, the frictional force does work (change ordered KE into TE)

How can we heat things up?? You add thermal energy to an object by doing work on the object: If a fuel burns, chemical energy is turned into TE

How is heat transferred?

CONDUCTION – atoms vibrate and bump into neighbors and change energy with neighbors CONVECTION – density changes with pressure (hotter objects decrease density in surroundings; thus less pressure and molecules rise) RADIATION – charged particles accelerate and emit Electromagnetic radiation and lose energy (vibrating particles are always accelerating since velocity Is always changing)

Calorimetry 10g of Al (25ºC) placed in 100mL of hot water (90ºC) in insulated chamber. What is the final temperature? Recall Q = mcΔT c (Al) = 0.91 g/J º c (water) = 4.19 g/J º

Calorimetry 10g of Al (25ºC) placed in 100mL of hot water (90ºC) in insulated chamber. What is the final temperature? (c Al =0.91 J/g ºC) Q (lost by water) = Q (gained by Al) -m w c w ΔT w = m Al c Al ΔT Al -(100)(4.19)(T f -90) = (10)(0.91)(T f -25) Tf = 88.7ºC

Terms Specific Heat Capacity (J/kg ºC) c p or c v Molar Heat Capacity (J/mol ºC) C Heat Capacity (J/ ºC) Specific Latent Heat (J/kg) – during phase change L f or L v

Calorimetry with Phase Changes L (vaporization) = 2256 kJ/kg L v * m L (fusion) = 334 kJ/kg L f * m C (water) = 4190 J/kg ºC C (ice) = 2100 J/kg ºC How much energy is required to change ice at -10 ºC to steam at 100 ºC? PHASE CHANGES!!!!

ANSWER Part 1: Heat ice from -10 ºC to zero Q = mc ice ΔT Part 2: Phase change from ice to water Q = L f * m Part 3: Heat water from 0 ºC to +100 ºC Q = mc water ΔT Part 4: Phase change from water to steam Q = L v * m

Thermal Expansion Consider a round object with a hole in the center When the object is heated, what happens to the hole (Expands? Contracts? Same size?)

Heat objects by doing work on the object, hmmm……. A cylindrical pump contains one mole of ideal gas. The piston is free to move, but no gas can leak out. Neglect friction between the piston and cylinder. The piston is quickly pressed IN as shown. The temperature of the gas increases. WHY?

Answers When you push the cylinder IN, you are doing work on the system, thus T increases. KE of the gas molecules increase when the piston hits the molecules

Flow of Heat Heat = dQ/dt What determines the flow of heat between two objects? HOT COLD L, length of tube r, radius of cylindrical tube

Flow of Heat Heat = dQ/dt For two objects: dQ/dt = kA (T H – T c )/L To measure experimentally: dQ/dt = mc dT/dt

Flow of Heat For a phase transition dQ/dt = L dm/dt (loss of mass due to evaporation)

Internal Energy (U) Sum of all energy of the molecules in an object (incl translational, rotational, and vibrational) from atomic collisions with a wall..... PV = 2/3 N U, but all the energy is KE so... PV = 2/3 N KE ave if you let T = 2/3 KE ave /k B or, KE ave = 3/2 k B T PV = N k B T = nRT

Boltzman Constant NOTE: N k B = nR k B = 1.38 x J/K molecule N = number of molecules n = number of moles (6.02 x molecules) For one mole of molecules: R = k B * N/n = 1.38 x * 6.02 x = 8.31 J/mole K

Internal Energy of Gases Change in internal energy per degree K MONATOMIC GAS: DIATOMIC GAS: additional energy from the rotation of the atoms around the bond 5