St18:Thermal Energy/Temperature

Thermal Energy = the total energy of all the particles in a substance. Unit for energy is the Joule http://www.bylandwaterandair.com/australia/alice_springs_nt_to_adelaide_sa/forest_fire_at_night

Thermal Energy To explain further: -The warmer an object gets, the more thermal energy(also: kinetic energy) it has. So what’s temperature?

http://study.com/academy/lesson/how-to-calculate-specific-heat-capacity-for-different-substances.html

Temperature vs. Thermal energy Temperature is related to the average kinetic energy of the particles in a substance.

Kelvin- (absolute temperature scale) Temperature Scales Celsius Fahrenheit 0 ºC- freezing* 32ºF- freezing 100 ºC- boiling* 212ºF- boiling (*in between are 100 equal parts called degrees) Kelvin- (absolute temperature scale) a. K = ºC + 273 Example:10 ºC = 283K b. ºC = K – 273 Example: 10K = -263 ºC Temperature has no upper limit!

Absolute Zero- Nature’s Lowest Possible Temperature At this temperature molecules have lost all available kinetic energy Can not get any colder

Recap: Thermal energy relationships a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased). b. At the same temperature, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

38 ºC (100ºF) 38ºC (100 ºF) Which has more Thermal energy?

1st Law of thermodynamics The gain or loss of thermal energy equals the amount of heat transferred

2nd Law of thermodynamics Heat never spontaneously flows from a cold substance to a hot substance In other words….heat always goes from hot to cold!

a. The flow of thermal energy from one object to another. Cup gets cooler while hand gets warmer Heat a. The flow of thermal energy from one object to another. b. Heat always flows from warmer to cooler objects. Ice gets warmer while hand gets cooler

3rd law of thermodynamics No system can reach absolute zero

St. 19: Specific Heat Capacity

Land heats up and cools down faster than water 6. Specific Heat a. Some things heat up or cool down faster than others. Land heats up and cools down faster than water

b. Specific heat is the amount of heat required to raise the temperature of 1 g of a material by one degree (C or K). 1) Cp water = 4.18 J / g ºC 2) Cp sand = .664 J / g ºC This is why land heats up quickly during the day and cools quickly at night and why water takes longer.

Water’s specific heat-controls climate

How to calculate changes in thermal energy H = m x T x C H = change in thermal energy m = mass of substance T = change in temperature (Tf – Ti) C = specific heat of substance

Practice Problems: Specific Heat Aluminum has a specific heat of .902 J/g C° How much heat is lost when a piece of Aluminum with a mass of 23.9 g cools from a temp of 415 C° to a temp of 27 C°.

St. 20- Thermal Equilibrium

Thermal Expansion When an object is heated, it expands. When object is cooled, it contracts. This is known (to physics-types) as THERMAL EXPANSION. as temperature increases molecules move faster (have a greater average translational KE) and move farther apart

Strange Thermal Expansion Water contradicts this idea when it is heated from 0⁰C to 4⁰C – it actually CONTRACTS. Water is the most dense at 4⁰C! This is why fish can live in a lake that has ice on top – the water at the bottom is 4⁰C. Remember, 0 ˚ C is 32 F So 4 ˚C is about 40 F

Thermal Equilibrium When two objects in thermal contact reach the same temperature No heat flows through between them!!

Ex: thermal equilibrium Thermometers measure air temperatures. Thermometers work because matter expands when heated. Most thermometers are closed glass tubes containing liquids such as alcohol.

http://www.youtube.com/watch?v=vcgYQ-u7qfc http://www.youtube.com/watch?v=YWJHNG5y5F0&feature=related

What would be the final temperature of the mixture of 50g of 20º water and 50g of 40º C water?

What would be the final temperature of 1 L of water at 20ºC and 2L at 40º C

Problem A jar of tea is placed in sunlight until it reaches an equilibrium temperature of 32oC. In an attempt to cool the liquid to 0oC, which has a mass of 0.l80 kg, how much ice at 0oC is needed? Assume the specific heat capacity of the tea to be that of pure liquid water.

m ice = (.180kg)(4186 J/kgoC)(32oC) 3.33x105 J/kg = 7.2 x 10-2kg m tea = 0.180kg m ice = ? which is the mass of the water that has melted cp tea = cp water = 4186 J/kgoC H f = 3.33 x 105 J/kg and t final = 32oC H lost = H gained tea loses and water gains only melting the ice (mcDt)tea = (mHf)ice m ice = (mcDt)tea Hf ice m ice = (.180kg)(4186 J/kgoC)(32oC) 3.33x105 J/kg = 7.2 x 10-2kg

St. 21- Methods of Heat Transfer

Methods of Energy Transfer 1. Conduction- energy transfer from particle to particle that are in CONTACT Conductors and insulators Transfer of energy is slow Works best in solids!

Examples of conduction Ice cube melts Metal spoon in boiling water

2. Convection Give energy to molecules then move the molecules based on density Works best in liquids and gases

Why is it windy at the seaside?

Why does hot air rise and cold air sink? Convection questions Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air. Why are boilers placed beneath hot water tanks in people’s homes? Hot water rises. So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

3. Radiation Heat from the sun Transmits without matter to carry energy Ex: Fireplace

The third method of heat transfer There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. How does heat energy get from the Sun to the Earth? ?

Absorb vs Emit Good absorbers are dark Ex: Pupil of eye Good absorbers are good emitters Good absorbers reflect very little Good Emitter/good absorber Poor emitter/ poor absorber Dull black surface Shiny silver surface Rough surface Smooth surface

Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? Shiny metal Dull metal Dull black Shiny black -The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. -The ________ container would be the coolest because it is the best at _______ heat radiation.

Absorption experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? Shiny metal Dull metal Dull black Shiny black The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.

1. Which of the following is not a method of heat transfer? A. Radiation B. Insulation C. Conduction D. Convection

2. In which of the following are the particles closest together? A. Solid B. Liquid C. Gas D. Fluid

3. How does heat energy reach the Earth from the Sun? A. Radiation B. Conduction C. Convection D. Insulation

Newton’s Law of cooling Rate of cooling is proportional to the temperature difference

Greenhouse Effect The warming effect whose cause is that short wavelengths enter the earth easier than long wavelengths exit the earth

St. 22- Phase Changes

A. Matter can exist in four phases: Solid, Liquid, Gas, and Plasma. Phases of Matter PLASMA A. Matter can exist in four phases: Solid, Liquid, Gas, and Plasma.

1. Vaporization-phase change from liquid to gas A. 1st type of Vaporization: evaporation- takes place at the surface COOLING PROCESS Higher energy leaves lower temp Perspiration

1. Vaporization B. 2nd Type of Vaporization : Boiling- bubbles of vapor form due to pressure

2. Sublimination Molecules jump directly from solid to gas Dry ice and snow

3. Condensation Change of a gas to liquid Warming process Kinetic Energy is absorbed

Melting Point From solid to liquid Add heat, molecules move faster, break bonds

Freezing point From liquid to solid Forming bonds

Between phase change, energy causes increase in temperature Between phase change, energy causes increase in temperature! During phase change no increase in temp