Mr. Bouyer

Day 1 | Day 2 | Day 3 | Lab | Vocabulary Test

Heat of fusion Heat of vaporization Melting point Freezing point Boiling point Thermal expansion Thermostat	Heating system Cooling system British Thermal Unit BTU R-Value Heat engine	External combustion Turbine Internal combustion Gasoline Four-cycle Two-cycle Diesel

Heat Changes in Matter

As a substance changes from one phase to another, there will be a change in heat energy but NO temperature change. This happens because all the energy in the system is being used to change the phase and not to change the speed of particle motion.

Heat of Fusion:

• The amount of heat needed to change one gram of a substance from the solid phase to the liquid phase.
• The H_fus of water is about 80 calories / gram.

Heat of Vaporization:

• The amount of heat needed to change one gram of a substance from the liquid phase to the gas phase.
• The H_vap of water is about 540 calories / gram.

Melting Point:
• The temperature at which a substance changes from the solid phase to the liquid phase.
• There is no change in temperature while this change of phase takes place.
Freezing Point:
• The temperature at which a substance changes from the liquid phase to the solid phase.
• There is no change in temperature while this change of phase takes place.

Boiling Point:
• The temperature at which a substance changes from the liquid phase to the gas phase.
• There is no change in temperature while this change of phase takes place.

Equations used to calculate heat: To change the temperature of a substance without changing phase: Heat, in calories = (mass) (temperature change) (specific heat) To change the phase of a substance from solid to liquid: Heat, in calories = (mass) (Hfus) To change the phase of a substance from liquid to vapor: Heat, in calories = (mass) (Hvap)

A typical problem involving change of phase and temperature:

• The problem: How much heat is needed to raise the temperature of 100 grams of water from ice at -25 ^oC to steam at 100 ^oC?
  • The following values are needed:
    • H_fus for water = 80 calories/gram
    • H_vap for water = 540 calories/gram
    • Specific heat of ice = 0.5 cal/g ^. C^o
    • Specific heat of water = 1 cal/g ^. C^o
    • Specific heat of water vapor = 0.25 cal/g ^. C^o

• The solution:

  1. First - Calculate the heat is needed to change the temperature of the 100 grams of ice from -25 ^oC to 0 ^oC using the equation

  H = (mass) (temperature change) ( specific heat)

  2. Second - With the temperature of the ice at 0 ^oC, calculate the heat needed to melt the ice using the equation

  H = (mass) ( H_fus)

  3. Third - You now have 100 grams of liquid water with a temperature of 0 ^oC. Calculate the heat needed to bring the temperature of the liquid water to 100 ^oC using the equation

  H = (mass) (temperature change) ( specific heat)

  4. Fourth - The temperature of the water is now 100 ^oC, calculate the heat needed to change its phase from liquid to gas using the equation

  H = (mass) ( H_vap)

  5. Finally - Add all the heat values together to answer the question.

  Practice problems: You continue to heat the water vapor. The heating device you are using produces 2000 more calories and runs out of fuel. What is the temperature of your water vapor now? How many Kilocalories were used to change 100 g of ice at -25 oC to 100 g of water vapor at 180 oC?

Homework Assignment 291:
This assignment must be turned in by the beginning of class tomorrow to receive credit.
Scoring criteria

The "values" needed for these problems are given in the sample problem above.

1. How much heat is needed to raise the temperature of 250 grams of water from -50 ^oC to -10 ^oC?

2. How much heat is used to raise the temperature of 1 liter of liquid water by 40 C^o?
   Hint: Be sure you understand the wording of this problem.

3. A sample of ice has a mass of 25 kilograms. Enough heat is added to the ice that it is eventually turned into steam. How much heat is used during just the phase changes that the sample goes through.

Day 2

When cooled, what common substance expands as it approaches its freezing point?

Compliance Officer

Thermal Expansion: The expansion of a substance due to Heat. Most substances expand when their temperature is increased and contract as they cool. Thermostat Contains a bimetallic strip that acts as a switch. This device can use temperature changes to turn a flow of electricity off and on.

Controlling the Environment:
Types of Heating Systems: Hot water system Steam system Radiant hot water system Radiant electric system Warm water system Hot air system Heat pump system Solar system Active Passive	Cooling Systems remove heat by evaporation using the following basic parts: Storage tank Freezer unit Compressor Condenser coils

Insulation is a poor conductor of heat thereby reducing the transfer of heat that occurs by conduction and convection. The effectiveness of building insulating materials is measured according to R-value.

British Thermal Unit, BTU

The BTU is an English standard unit of energy. It is often used as a quantitative unit for the energy-producing or energy-transferring capability of heating and cooling systems such as furnaces, ovens, refrigerators, and air conditioners.

One BTU is the amount of thermal energy necessary to raise the temperature of one pound of liquid water by one degree Fahrenheit at the temperature at which water has its greatest density (39 degrees Fahrenheit).

One BTU is approximately equal to:

252 calories 778 foot-pounds 1055 joules 108 kilogram-meters 0.0003 kilowatt-hours

One pound (0.454 kilogram) of coal should yield 14,000 to 15,000 BTU; a pound of gasoline or other fuel oil, approximately 19,000 BTU.

Day 3

What part of an internal-combustion engine turns linear motion into rotational motion?

Heat engines are machines that burn some type of fuel to produce heat, then convert the heat energy into mechanical energy. Most heat engines burn gasoline to produce heat. In addition to the fuel, large amounts of air are needed for combusion.

Two types of heat engines:

1. External-Combustion Engine:
Fuel is burned outside the engine.

Turbine

2. Internal-Combustion Engine:
Fuel is burned inside the engine.

Four-Cycle (strokes):

1. Intake
2. Compression
3. Power
4. Exhaust

Two-Cycle (strokes):

1. Intake and Power
2. Compression and Exhaust

Diesel Engine:

Any volunteers may ask the science facilitator for tools and remove the #1 piston from the Chevy 350 V-8 engine in the classroom.

Test Your Concept Understanding: Write at least one paragraph explaining why a two-cycle engine is less efficient than a four-cycle engine. Write at least one paragraph explaining why two-cycle engines continue to be made, even though they are inefficient. Use this website to answer the following questions: State and federal taxes accounted for what percent of the price of a gallon of gasoline in 2000? Why do gasoline prices fluctuate? Why do gasoline prices differ according to region?

Research Links:

• Internal Combustion Engine - Washtenaw Community College, Ann Arbor MI
• All About Autos / Repairs and Maintenance - Autosite.com
• Oil and Gas Reference Tools - Independent Petroleum Association of America
• Current Gasoline Prices - Energy Information Administration

Physical Science

1. H = (mass) (Temp Change) ( Specific Heat)
H = (100 g) (25 C^o) (0.5 cal/g ^. C^o)
H = 1250 calories

2. H = (mass) ( H_fus)
H = (100 g) (80 cal/g)
H = 8000 calories

3. H = (mass) (Temp Change) (Specific Heat)
H = (100 g) (100 C^o) (1 cal/g ^. C^o)
H = 10000 calories

4. H = (mass) ( H_vap)
H = (100 g) (540 cal/g)
H = 54000 calories

A. H = (mass) (Temp Change) ( Specific Heat)
You must manipulate the equation to yield Temperature Change
Temp Change = calories of heat / (mass) (Specific Heat)
Temp Change = 2000 calories / (100 g) (0.25 cal/g ^. C^o)
Temp Change = 80 C^o
Final Temperature = 100 ^oC + 80 C^o
Final Temperature = 180 ^oC

B. 1250 cal + 8000 cal + 10000 cal + 54000 + 2000 cal = 75250 calories
75250 caloreis / 1000 calories per Kilocalorie = 75.25 KCAL

The temperature of a substance (ice in this case) does not change during a phase change because all the extra heat is used to change the phase. Ice absorbs heat from the water as it melts. This causes the water to get "cold" (have less heat).

As water cools, it contracts until it reaches 4 ^oC, then it will expand until it freezes at 0 ^oC.
This property causes pipes to break when the water in them freezes.

In an internal-combustion engine, the crankshaft changes linear motion into rotational motion.
Pistons move up and down (linear) during combustion. Because of their offset connection to the crankshaft, as the pistons move up and down, the crankshaft rotates.

Once rotational motion is achieved, the only thing left to be done is change the direction of rotation to make an automobile move.