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2.1 Energy

Potential energy = energy due to position a compressed spring chemical bonds in gasoline, coal, or

food 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.

The total energy of an object (system) is the sum of its Ek and Ep

Et = Ek + Ep

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All objects possess Thermal energy which is the potential and kinetic energies associated with the random motion of the atoms and molecules within an object that results in the system temperature.

Hot coffeeHigher thermal energyTemperature is high

Cold coffeeLower thermal energyTemperature is low

time

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

The transfer of thermal energy is called heat and symbolized q.

Heat lost by the coffee = -q Heat gained by the room = +q

Heat = energy in transit, from one system to another due to a temperature difference.

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

thermometer.

Heat can be transferred from one substance to another.

Temperature = a quantitative description of hotness or coldness

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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. WhatIs 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 the following units:

a. calories b. kilojoules

Practice

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?

3. A dermatologist may use cryogenic liquid nitrogen at –196 ˚C to remove skin lesions and some skin cancers. What is the temperature of the liquid nitrogen in K?

4. State the temperature, including the estimated digit, on each of the following Celsius thermometers:

Practice

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The amount of heat transferred, depends on 3 factors:

o The specific heat :WaterGoldSteel

o The T change of the substance:∆T = 0.001 ˚C∆T = 1000 ˚C∆T = 1000000 ˚C

o The amount of substance:10 g100g1000g

= Tf - T

i= 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

Water 4.184 JAluminum 0.897 J

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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: Need:

750 g of water ? heat transferred

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 Δ T: 65 °C – 37 °C = 28 °C

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

Example---using the heat equationWhat is the specific heat of a metal if 24.8 g absorbs 65.7 cal of

energyand the temperature rises from 20.2 ° C to 24.5 ° C?

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STEP 1

Given: Want:

mass 24.8 g, ? SH metal

heat 65.7 cal,Ti 20.2 ° C Tf 24.5 ° C

STEP 2 Plan:

STEP 3 execute: ΔT = 24.5 ° C – 20.2 ° C = 4.3 ° C

65.7 cal = 0.62 cal/g ° C (24.8 g)(4.3 ° C)

Conversion factororequation

Heat = mass x Δ T x SH

Food = EnergyPotential Energy

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.

120 Cal x 1000 cal x 4.184 J = 502,080 J

1 Cal 1 cal 500 kJ

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Nutritional calorie (Cal) = 1 kcal = 1000 cal

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

2 million cal

Eating 14 crackers provides 120 Cal.4 g fat x 9 Cal/g = 36 Cal19 g carbs x 4Cal/g = 76 Cal2 g protein x 4 Cal/g = 8 Cal

120 Cal

% fat = 35 x 100 = 29%120

Practice

6. 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

7. Ethanol has a specific heat of 2.46 J/g °C. When 655 J are added to a sample of ethanol, its temperature rises from 18.2 ˚C to 32.8 ˚C. What is the mass in grams of the ethanol sample?

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5. What is the specific heat of lead if 13.6 cal are needed to raise the temperature of 35.6 g of lead by 12.5 ºC?

8. 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? Round off the kilocalories for each food type to the tens place.

9. Use table 2.12, to determine the number of hours of running needed to burn off the calories in this meal.

Practice

02_T07.JPG

2.5 Classification of Matter

THREE STATES OF WATER

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 do not change.

2.6 STATES AND PROPERTIES OF MATTER

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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.

q = m ΔH

2.7 Changes of State

When energy is absorbed by a solid or liquid, the T of the sample does not necessarily rise. Instead, the sample may change from one state to another.

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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

is the amount of heat needed to melt 1 gram of a solid

is the amount of heat released when 1 gram of liquid freezes

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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 = ΔHvFor water: = 2260 J or 540 cal

1 g of water

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

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

Boiling Point of Water = 100 °C

02_13.JPG

A cooling curveillustrates the changes of state as a gas is cooleduses sloped lines to indicate a decrease in temperatureuses 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

02_13-15UN.JPG

Using the graph, determine the following:

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

16. The physical change taking place in the plateaus.

Practice

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

1) a temperature change

2) a constant temperature

3) a change of state

12. How many plateaus are there on the graph?

13. A sloped line on a heating curve represents

1) a temperature change

2) a constant temperature

3) a change of state

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

02_13-16UN.JPG

Assign the corresponding beaker number to a letter on the graph

17. Using the graph, determine the following:

Practice

18. Practice (HW problem #51 a)

Using the values for the heat of fusion, specific heat of water, or heat of vaporization, calculate the amount of heat energy in each of the following:a. calories needed to warm 20.0 g of water at 15 ˚C to 72 ˚C

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