Energy

Potential energy

= energy due to position, condition, or composition.

o a compressed springo chemical bonds in gasoline, coal, or

foodo Gravitational potential energy (due to

mass and height)

Kinetic Energy

= energy due to movement.

o Bullet

o Water flowing over a dam

o Steam

There are many forms of energy: solar, electrical, nuclear, mechanical...... but only two types:

The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed.

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The Kinetic energy associated with the random motion of molecules is called Thermal energy.

The amount of thermal energy in an object is given by its temperature.

Hot coffeeTemperature is highHigher thermal energy

Cold coffeeTemperature is lowLower thermal energy

time

The change in temperature is due to a transfer of thermal energy from the coffee (system) to its surroundings (room).

Heat = transfer of thermal energyfrom one system to another due to a temperature difference.energy in transit

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To use temperature as a measure of hotness or coldness, we need to construct a temperature scale. This is what we call a thermometer.

Temperature = a quantitative description of hotness or coldness

1.8, 32 and 273 are defined numbers and therefore are exact numbers

To convert from one T scale to another:

Example -- Solving a Temperature Problem

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TF = 1.8 (TC) + 32 °

TF = (1.8) (34.8 °C) + 32 ° exact 3 sf

= 62.6 ° + 32 ° 1 decimal pl. exact

= 94.6 °F 1 decimal pl.

A person with hypothermia has a body temperature of 34.8 °C. What is that temperature in °F?

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EnergyUnits

calorie

joule

the amount of heat required to raise the T of 1g of water by 1 ˚C

In honor of 19th century English physicist Prescott JouleSymbol is capital JPronounced “jewel”

1 cal = 4.184 J(exactly)

At the beginning, scientist started to measure heat in terms of its ability to raise the T of water.

In 1948, scientists decided that since heat (like work) is transferred energy, the SI unit of heat (the joule) should be the one to use for energy.

The calorie is now defined to be 4.184 J, with no reference to the heating of water.

The “calorie” used in nutrition, sometimes called the Calorie (Cal), is really a kilocalorie.

1 Cal = 1 kcal = 1000 cal.

2.1

1. When 1.0 g of octane fuel burns in an automobile engine, 48 000 J are released. Convert this quantity of energy to calories:

2. In a type of cancer treatment called thermotherapy, temperatures as high as 113 ˚F are used to destroy cancer cells. What is that temperature in degrees Celsius?

Practice

3. State the temperature (˚C), including the estimated digit.

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The amount of heat transferred, depends on 3 factors:

o The specific heat :WaterGold

o The T change of the substance:∆T = 0.001 ˚C∆T = 1000000 ˚C

o The amount of substance:10 g1000g

o The nature of the substance Ability of a specific material to incorporate (absorb) heat

It takes twice the amount of heat to boil 2 cups of water than 1 cup

It take more heat to raise the T by 100 degrees than by 10 degrees

= Tf-Ti

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Practice---using the heat equation

A hot-water bottle contains 750 g of water at 65 °C. If the water cools to body temperature (37 °C), how many calories of heat could be transferred to sore muscles?

STEP 1 Given: Want:

750 g of water ? heat

cools from 65 °C to 37 °C

Conversion factororequation

STEP 2 plan: Heat = mass x Δ T x SH

STEP 3 execute: the temperature change ΔT

65 °C – 37 °C = 28 °C

750 g x 28 °C x 1.00 cal = 21 000 cal g °C

The FDA recommends 30% of total intake from fat calories.For a female adult the level is around 2,000 calories per day, with 600 fat calories.For a male adult the level is around 2,500 calories per day, with 750 fat calories.

Food = EnergyPotential Energy

Nutritional calorie (Cal) = 1 kcal = 1000 cal

2000 Cal = 2000 kcal = 2,000,000 calories

2 million cal

4. How many kilojoules are needed to raise the temperature of 325 g of water from 15.0 °C to 77.0 °C?

1) 20.2 kJ

2) 84.3 kJ

3) 105 kJ

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Practice

5. At a fast-food restaurant, a hamburger contains 37 g of carbohydrate, 19 g of fat, and 24 g of protein. What is the energy content for each food type and the total energy content, in kcal?

6. Use table 3.10 to determine the number of hours of running needed to burn off the calories in this meal.

Classification of Matter

SolidLow E stateNo movementRigid structure

LiquidIntermediate EMore movement of particles

GasHigh ELots of movementParticles are free from one another

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Physical change Physical change

Physical change the identity and composition of the substance does not change.

THREE STATES OF WATER

The amount of heat per unit mass that must be transferred for a sample to completely undergo a phase change is called heat of transformation, ΔH. ΔH = q q = heat

m

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Melting = change from the solid state to liquid state.Heat is required to free particles from their rigid structure.

The heat of fusion= ΔHf

For water: 334 J or 80. cal 1 g of water

heat released when liquid freezes

heat needed to melt a solid

the amount of heat

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vaporizing = change from the liquid state to vapor (gas) state.Heat is required to free particles from one another.

The heat of vaporization = ΔHv

For water: = 2260 J or 540 cal 1 g of water

released when 1 g of a gas condenses to liquid at the boiling point

Normal Boiling Point of Water = 100 °C

absorbed to vaporize 1 g of a liquid to gas at the boiling point

A cooling curveillustrates the changes of state as a gas is cooleduses sloped lines to indicate a decrease in temperature uses plateaus (horizontal lines) to indicate a change of state

A heating curveillustrates the changes of state as a solid is heateduses sloped lines to show an increase in temperatureuses plateaus (horizontal lines) to indicate a change of state

To calculate the heat involved in a plateau q = m ΔH

ΔH f = heat of fusion = 80. cal/g

ΔH v = heat of vaporization =540 cal/g

Heat added

100 ˚C

0 ˚ C

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To calculate the heat involved in a slope q = m x ΔT x SH

water

Using the graph, determine the following:

11. The physical state of the substance present in the sloped lines.

12. The physical change taking place in the plateaus.

7. A plateau (horizontal line) on a heating curve represents

1) a temperature change

2) a constant temperature

3) a change of state

8. How many plateaus are there on the graph?

9. A sloped line on a heating curve represents

1) a temperature change

2) a constant temperature

3) a change of state

10. How many sloped lines are there on the graph?

Practice

13. Use the graph to assign a beaker number to a letter on the graphPractice

14. Using the values for the heat of fusion, specific heat of water, or heat of vaporization, calculate the amount of heat needed to warm 20.0 g of water at 15 ˚C to 72 ˚C

15. A sports trainer applies an ice bag to the back of an injured athlete. Calculate the heat, in kilocalories, that is absorbed if 155 g of ice at 0.0 ˚C is placed in an ice bag, melts, and rises to body temperature of 37.0 ˚C.

Practice