What effects heat transfer? For each of the 3 things that effect heat transfer (mass, material, and temperature difference) determine how each effects heat transfer on the molecular level.
What effects heat transfer? Mass – mass measure how many molecules there are to move. More molecules requires more energy to move them.
What effects heat transfer? Material – The types of bonds and arrangement of the molecules effects how the heat energy can be exchanged between each molecule. Solids are tightly packed and can exchange energy easily. (LOW specific heat) Liquids less easily. Water has hydrogen bonding which keeps the molecules from moving and is difficult to transfer energy. (HIGH specific heat)
What effects heat transfer? Delta T – Difference in energy levels means a different amount of energy transfer during each molecular collision.
What is heat? A form of energy. Flow of energy from one object to another due to temperature difference. How does heat energy move? Conservation of momentum. Molecular collisions. What is energy? The ability to do work. Can energy be created? No, it can only change forms; not be created nor destroyed. Where does energy come from? Motion of all atoms and molecules transferring energy from one to another.
Conservation of Energy (First Law of Thermodynamics) Energy CANNOT be created nor destroyed It can change forms. So, what are some forms of energy? How many can you name?
We will focus on these. Potential Energy Kinetic Energy Thermal Energy (Heat) Chemical Energy
Units of Energy Units of Heat calorie (c) Calorie (C) – Big “C”, Food Calories = 1,000 calories (little “c”)
Units of Energy Units of Heat Joules (J) = It is equal to the work done when applying a force of one newton through a distance of one meter. Newton (N) = unit of force Meter (m) = unit of distance J = N*m We will use Joules for Units of HEAT.
HEAT Is the COLD getting in or is the HEAT getting out?
HEAT HEAT is the transfer of energy from a hot object to a cold object.
What is going on here? Black Blocks
Specific Heat The specific heat is the amount of heat per unit mass required to raise (or lower) the temperature by one degree Celsius. Unit = J / Kg C
Specific Heat The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. Unit = J / Kg C Example – Spoons Which spoon increases Temperature faster? Which spoon has lower specific heat? Insulator Conductor
Specific Heat The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. Why do solids have low specific heat? Solids have closely packed atoms. Vibrations are quickly transferred to the next atom. Liquids have higher specific heat due to the vicinity of the atoms to each other and intermolecular forces.
Find the Trend! Water has a very high specific heat.
Why is the desert hot in the day and cold at night?
What type of climate is typically found near the coast?
What creates the wind? Ocean Breezes Water has higher specific heat than land so, Water retains heat longer Day – Wind from Ocean Night – Wind from land Explain? Why is it calm in the morning and evening?
Bell Ringer What is specific heat? Can you have negative heat flow?
Heat Transfer (Q)
Heat Transfer Practice Problems c = specific heat capacity (4.186 for H2O) in J/(g C) c = specific heat capacity (4186 for H2O) in J/(Kg C) How much energy is needed to warm up 300 kg of water from 10 C to a comfortable 37 C? What final temperature will be attained by a 250 g sample of Cu at 10 C if it absorbs 1000J of heat? Cu 's c = 0.39 J/(g C) What final temperature will be attained by a 250 ml cup of 10 C water if it absorbs 1000 J of heat? Note, because water's density = 1 g/mL, 250 mL = 250 g
Exothermic, Endothermic COLD to the touch, absorbs heat, q>0, Heat ENTERS HOT to the touch, emits heat, q<0, Heat EXITS
Energy is conserved. The energy lost by one object is gained by the other. Q = -Q mc (T f - T i ) = -mc (T f - T i )