# Temperature “How hot or cold something is”

## Presentation on theme: "Temperature “How hot or cold something is”"— Presentation transcript:

Temperature “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 K 0 K – Absolute zero

Temperature Scales

Internal Energy Grand total KE & PE inside a substance.
Depends on temp & amount of substance. Which beaker has more internal energy? Why?

Heat Amount of internal energy required to change temp.
A substance does not contain heat – it contains internal energy.

Heat Thermal 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 = Qgained There is no net change in energy! Energy is conserved!

Changes in Heat The internal energy changes when heat flows into or out of objects. Q = mc∆t Q = heat transferred (calories or joules) m = mass (g) C = specific heat (cal/g-°C) or (J/g-°C) ∆t = change in temp. (°C)

Specific 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 Materials Substance Specific Heat (cal/g-°C) Water 1.00 Wood .42 Aluminum .22 Glass .16 Iron .11 Copper .09 Silver .06 or J/g-°C

Units of Heat calorie - the amount of heat needed to raise the temperature of 1 g water 1 °C. Kilocalorie = Calorie (food unit). 1 Kcal = 1000 calories Joule J = 1 calorie.

Calculate Heat Transferred
How much energy would it take for 1 kg of aluminum to change from 22 °C to 32 °C? Q = mc∆t Q = 1000 g · .216 cal/g-C · 10 °C Q = 2,160 calories

Calculate 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∆t Q = 220 g · 1 cal/g-C · 80 °C Q = 17,600 calories

Methods 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 = QG mc∆t = mc∆t (50g)(c)(72 °C) = (100 g)(1.0cal/g ·°C)(8 °C) c = .22 cal/g ·°C aluminum

Methods of Mixtures A 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 = QG mc∆t = mc∆t (50 g)( .11 cal/g·°C)(40°C)=(200g)( 1cal/g°C)(∆T) ∆T = 1.1 °C 22 °C °C = °C is Tf

Methods of Mixtures Jerry 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 = QG mc∆t = mc∆t (350 g) ( .09 cal/g·°C) (20°C) = (1250g) ( 1cal/g°C) (∆T) ∆T = .504 °C 18 °C °C = °C is Tf

Mechanical Energy Relates to motion Potential Energy = mgd
Kinetic Energy = ½mv2 Work = F x d W = PE = KE Unit: Joule (J)

Thermal Energy Relates to motion of molecules Q = mc∆t
Unit: calorie or Joules

Conservation of Energy
Energy can’t be created or destroyed, but can change forms, including between thermal and mechanical. Elost = Egain Qlost = Qgain KE = Qgain PE = Qgain W = Qgain

Mechanical Equivalent of Heat
Relationship of mechanical energy to thermal energy. W = PE = KE = Q 1 calorie = J

Mechanical – 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 = Q mgd = mc∆t 5 kg · 9.8 m/s2 · 10 m = 5 kg · 670 J/kg-°C · ∆t ∆t = 0.15 °C

Thermal Expansion Expansion of a substance due to heat.

Phase Expansion ↑heat energy - ↑kinetic energy - ↑motion.
Gas/Liquid/Solid ↑temperature – expand ↓temperature – contract

Thermal Exp. of Water As 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.

Uses of Thermal Exp. Thermometer Sidewalk joints Building materials
Thermostat – bimetallic strip Consequences??

Expansion Rates Different materials expand at different amounts with the same temperature rise. Thermal Coefficients for Length & Volume. Solids (length) L = LO x  x T L = change in length L0 = original length  = coefficient of linear expansion T = change in temperature

Linear Expansion Coefficients
Material Coefficient ( C –1 ) Aluminum x 10-6 Brass x 10-6 Copper x 10-6 Glass x 10-6 Gold x 10-6 Iron (Soft) x 10-6 Lead x 10-6 Quartz x 10-6 Steel x 10-6

Expansion Rates The 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