Energy

Temperature

Energy

Heat

Learning objectives

• Perform conversions among different

scales of temperature

• Define energy and distinguish among types

of energy

• Perform simple energy calculations using

different energy units

• Apply specific heat concept to heat

calculations

• Determine caloric contents of food stuffs

based on composition of macronutrients

Temperature is the

measure of hotness

• A fundamental unit. There

are three(3) temperature

scales

BPH20

FPH2O

Difference

(1) Fahrenheit (oF)

212° 32° 180°

(2) Celsius (centigrade) (oC)

100° 0° 100°

(3) Kelvin (K)

373 273 100

Temperature

conversions

• Conversion:

Kelvin to Celsius (K -> ºC) ºC = K - 273

Celsius to Kelvin (ºC -> K) K = ºC +

273

Celsius to Fahrenheit (ºC -> ºF)

i multiply ºC x 9/5

ii Add ºC x 9/5 + 32

Fahrenheit to Celsius (ºF -> ºC)

i add ºF - 32

ii multiply (ºF - 32) x 5/9

Working with temperature

conversions

Heat and chemical

reactions

• The burning candle is

a chemical reaction

• It releases energy

that heats the air

molecules

• Heat is flow of energy

from a higher to a

lower temperature

Energy from chemical

reactions performs work

• Energy is capacity to do work

• In what way is a human like a

car?

• Both burn fuel to run

• Humans burn glucose

• C6H

12O

6+ O

2= CO

2+ H

2O

• Cars burn petrol

• C8H

18+ O

2= CO

2+ H

2O

Energy comes in many

forms

• Kinetic energy is energy due to motion

• Heat

• Rotation

• Vibration

• Translation

• Potential energy is energy due to position

or state

• Height

• Chemical

• Electrical

• Coiled spring

Energy can be

converted

• Processes convert

energy from one form

to another

• Falling down stairs

• (potential → kinetic

→ pain)

• Chemical reaction

• (potential →

heat/light)

• Battery

• (potential →

electrical)

• Engine

• (potential → heat →

kinetic)

But it never goes away

• Energy is conserved in any

process

• None is lost

• None is gained

• Law of Conservation of Energy:

Energy is neither created nor

destroyed in a chemical

reaction

Perpetual motion is a thing

of smoke and mirrors

• Visit the

museum of

unworkable

machines to

view a history of

conmen and

failure

Measuring energy: calories,

Calories and joules

• calorie is energy

required to raise

temperature of 1 g of

water 1 degree C

• Calorie is the food

version = 1,000 cal

• Raises temperature of

1 pint of water 3.8ºF

• Joule is SI unit derived

from mechanical work:

work done when force

of 1 Newton is applied

for 1 meter

1 cal = 4.18 J

Common energy

conversions

• 10 g of octane is burnt to produce

8500 J. How much is that in

calories? 1 cal = 4.18 J

Specific heat (capacity)

• Specific heat (capacity): energy required

to raise temperature of 1 g of substance

by 1ºC

• Units are J/gºC or cal/gºC

Champagne from a

styrofoam cup: Measuring

heat change• Calorimetry is process

used to measure heat

change of reaction

• Heat change in

calorimeter is:

Q = mH2O

x ΔTH2O

x SHH2O

Weigh Measure Know