Chapter 6

Big Question #1 How is heat related to an object’s mass and temperature?

Temperature Mass is the amount of substance in an object Temperature is defined as the measure of the average kinetic energy of the molecules in a sample.

Temperature Scale ScaleWater Freezes Water Boils Who Uses Fahrenheit Celsius Kelvin 273 K373 K Absolute temp. Used in some formulas. 32°F 0°C0°C 212°F 100°C U.S. & one other country Everyone else. Scale used often in science

Changes in Thermal Energy 1)Temperature  AVERAGE KE of a sample 2)Thermal Energy  sum (total) of all KE and PE of the molecules in a substance (PE comes from energy in bonds) a) depends on: 1) mass  amount of matter 2) temperature 3) amount of energy the material can hold

Heat 1)Thermal Energy  sum (total) of all KE and PE of the molecules 1)(PE comes from chemical energy in bonds) 2)Heat is defined as the flow of thermal energy.

Heat 1)Heat only exists where there is a difference in temperature. eat flows from hot to cold 2)Unit of heat is the calorie. a) calorie is defined as the quantity of heat needed to raise the temperature of 1 gram of water by 1°C

Specific Heat 1)Defined as a property of a substance that tells how much the temperature goes up when a given amount of heat is applied. 2)How hard is it to raise the temperature of a material 3)The higher the specific heat, the harder it is to raise the objects temperature

SubstanceSpecific Heat calorie/g°C Water1.00 Ice0.493 Aluminum0.215 Silver0.052 Gold0.031 Very difficult to raise the temp of water, reason why water is used as a coolant Easy to raise the temp because of the low specific heat

Big Question #1 How is heat related to an object’s mass and temperature? The more heat that is put in, the more the temperature increases. The more heat that is lost, the more the temperature decreases. The more mass an object has, the less (or more slowly) the temperature increases. The less mass an object has, the more(or quicker) the temperature increases. Specific Heat can show how hard it is to change a substance’s temperature

The Heat Equation Q = mcΔT Heat energy (calorie) Mass (g) Specific Heat (calorie/g°C) Change in temp (°C) ΔT = T f – T i If ΔT is negative = heat is lost, Q is negative If ΔT is positive = heat was gained, Q is positive

Q = mcΔT Sample Problem: How much heat is needed to raise the temp of 250 g of water from 20°C to 40°C? Q = ?? m = 250 g c = 1.00 calorie/g°C ΔT = 40 – 20 = 20°C Q = (250)(1.00)(20) Q = 5000 calories

When 300 calories of energy is lost from a 125g object, the temp decreases from 40 to 45C. What is the specific heat of this object? Q = -300 calories m = 125 g c = ?? ΔT = 40 – 45 = -5°C -300 = (125)(c)(-5) -300 = (c)(-625) -300 = c = c

1200 calories of heat energy is added to a liquid with a specific heat of If the temperature increases from 20 to 33°C, what is the mass of the object? Q = 1200 calories m = ??? c = 0.57 calorie/g°C ΔT = 33 – 20 = 13°C 1200 = (m)(0.57)(13) 1200 = (m)(7.41) g = m = m

Big Question #2 How does Heat flow and how can materials react?

Flow of Heat and Equilibrium 1)First Law of Thermodynamics  energy in a closed system is conserved heat loss = heat gain When the ice cube goes into the coffee, the amount of heat lost by the coffee will equal the heat gained by the ice cube.

2) Thermal Equilibrium  two objects are at the same temperature. a) Heat always flows from hot to cold. b) Heat flow stops once objects reach thermal equilibrium.

Calculating Equilibrium Temp Sample Problem grams of water at 85°C is mixed with 100 grams of water at 45°C. What is the resulting temp of the mixture?

Calculating Equilibrium Temp Sample Problem grams of water at 65°C is mixed with 200 grams of water at 90°C. What is the resulting temp of the mixture?

Thermal Expansion 1)Most materials expand when heated because the molecules move apart 2)Thermal expansion is the principle behind thermometers. a) expansion of the liquid inside the tube is proportional to the change in temperature 3) Thermal expansion is used in thermostats. a) Thermostats use a bimetallic strip to open and close the circuit.

Big Question #2 How does Heat flow and how can materials react? Heat flows from a hot object to a cold one until thermal equilibrium is reached. Most objects will expand when heated. This principle is important for thermostats and thermometers.