Presentation on theme: "Temperature “How hot or cold something is”"— Presentation transcript:
1Temperature “How hot or cold something is” Measures avg. K.E. of the particles in the object.Tool: thermometer – meas. in degrees.Scales~ Celsius (°C) 0° - 100°~ Fahrenheit (°F) 32° - 212°~ Kelvin (K) 273 K – 373 K0 K – Absolute zero
3Internal Energy Grand total KE & PE inside a substance. Depends on temp & amount of substance.Which beaker has more internal energy? Why?
4Heat Amount of internal energy required to change temp. A substance does not contain heat – it contains internal energy.
5HeatThermal Contact – objects in contact or mixed. Heat flows from higher temp. substance to low temp. substance.Thermal Equilibrium – thermal contacts reach same temp. – no heat flow.Qlost = QgainedThere is no net change in energy! Energy is conserved!
6Changes in HeatThe internal energy changes when heat flows into or out of objects.Q = mc∆tQ = heat transferred (calories or joules)m = mass (g)C = specific heat (cal/g-°C) or (J/g-°C)∆t = change in temp. (°C)
7Specific Heat Capacity Ability of a sub. to store internal energy.The amount of heat needed to raise the temp. of 1 g of the material 1 °C.Units: cal/g-°C.Specific Heat of MaterialsSubstanceSpecific Heat (cal/g-°C)Water1.00Wood.42Aluminum.22Glass.16Iron.11Copper.09Silver.06orJ/g-°C
8Units of Heatcalorie - the amount of heat needed to raise the temperature of 1 g water 1 °C.Kilocalorie = Calorie (food unit).1 Kcal = 1000 caloriesJoule J = 1 calorie.
9Calculate Heat Transferred How much energy would it take for 1 kg of aluminum to change from 22 °C to 32 °C?Q = mc∆tQ = 1000 g · .216 cal/g-C · 10 °CQ = 2,160 calories
10Calculate Heat Transferred Let’s compute how much energy it takes to make a cup of coffee or tea. Eight ounces of water has a mass of 0.22 kg. How much heat must be transferred to water to raise its temperature from 20 °C to 100 °C?Q = mc∆tQ = 220 g · 1 cal/g-C · 80 °CQ = 17,600 calories
11Methods of Mixtures mc∆t = mc∆t A 50 g piece of metal immersed in boiling water is placed in 100 g of water at 20 °C. The final temperature of metal and water is 28 °C. What is the specific heat of the metal? What is the metal?QL = QGmc∆t = mc∆t(50g)(c)(72 °C) = (100 g)(1.0cal/g ·°C)(8 °C)c = .22 cal/g ·°C aluminum
12Methods of MixturesA 50.0 g block of iron at 80 C is dropped into a cup of 200 g of water at 22 C. The block cools to 40 C. What would be the temperature change of the water?QL = QGmc∆t = mc∆t(50 g)( .11 cal/g·°C)(40°C)=(200g)( 1cal/g°C)(∆T)∆T = 1.1 °C22 °C °C = °C is Tf
13Methods of MixturesJerry grabs a hot g brass spoon from his bowl of soup, originally at a temperature of 95.0 C. To avoid burning his fingers he drops the spoon into a sink of 1,250 g water at 18.0 C. One second later, the spoon has cooled to a temperature of 75.0 C. Calculate the temperature of the water at this time.QL = QGmc∆t = mc∆t(350 g) ( .09 cal/g·°C) (20°C) = (1250g) ( 1cal/g°C) (∆T)∆T = .504 °C18 °C °C = °C is Tf
14Mechanical Energy Relates to motion Potential Energy = mgd Kinetic Energy = ½mv2Work = F x dW = PE = KEUnit: Joule (J)
15Thermal Energy Relates to motion of molecules Q = mc∆t Unit: calorie or Joules
16Conservation of Energy Energy can’t be created or destroyed, but can change forms, including between thermal and mechanical.Elost = EgainQlost = QgainKE = QgainPE = QgainW = Qgain
17Mechanical Equivalent of Heat Relationship of mechanical energy to thermal energy.W = PE = KE = Q1 calorie = J
18Mechanical – Thermal Energy A 5 kg concrete block falls 10 m to the ground. If all of the block’s energy is converted into heat that is absorbed by the block only, it’s temperature is raised _____?PE = Qmgd = mc∆t5 kg · 9.8 m/s2 · 10 m = 5 kg · 670 J/kg-°C · ∆t∆t = 0.15 °C
19Thermal ExpansionExpansion of a substance due to heat.
20Phase Expansion ↑heat energy - ↑kinetic energy - ↑motion. Gas/Liquid/Solid↑temperature – expand↓temperature – contract
21Thermal Exp. of WaterAs the temp. decreases from 4°C to 0°C, water expands - ice.Its density decreases.The maximum density of water (1.0 g/mL) occurs at 4°C.
22Uses of Thermal Exp. Thermometer Sidewalk joints Building materials Thermostat – bimetallic stripConsequences??
23Expansion RatesDifferent materials expand at different amounts with the same temperature rise.Thermal Coefficients for Length & Volume.Solids (length) L = LO x x TL = change in lengthL0 = original length = coefficient of linear expansionT = change in temperature
24Linear Expansion Coefficients Material Coefficient ( C –1 )Aluminum x 10-6Brass x 10-6Copper x 10-6Glass x 10-6Gold x 10-6Iron (Soft) x 10-6Lead x 10-6Quartz x 10-6Steel x 10-6
25Expansion RatesThe Eiffel Tower, constructed in 1889 by Alexandre Eiffel, is an impressive latticework structure made of steel. If the tower is 301 m high on a 22 oC day, how much does its height decrease when the temperature cools to 0.0 oC?L = LO x x T= 301 m • 10.5 x10-6 • 22 °C= m