Transcript Energy and Temperature

Energy
What is energy and how does it fit
into chemistry?
Energy is the capability to do work.
Many chemical reactions either create or release
energy when they occur.
 Forms of energy include:


–
–
–
–
–
–
Chemical – energy stored in chemical bonds
Mechanical – energy involved in motion
Electrical – energy involved in electricity
Light – energy that involves light
Sound – energy that involves sound
Heat – energy transferred between objects that are
different temperatures
Energy Transfer

Energy can be transferred in numerous ways:
– Electric current in a wire – electrical energy
– Beam of light – light energy
– Peddling a bicycle – mechanical energy
– A candle – thermal and light energy
Gasoline is placed into your car. The engine of
your car ignites the gasoline to produce heat.
The heat it creates, makes the gases expand
that push pistons, which makes your car move.
 Chemical (gas)  heat  mechanical

So, as you can see, energy
is usually transferred from
one type of energy to
another
The Energy Law

Law of conservation of energy
– During any physical or chemical change, the
total quantity of energy remains constant
– In other words, energy cannot be created or
destroyed.
Environment
around the
Experiment
Location of the
Experiment
Total amount stays the same; it is just
transferred from system to surroundings
Endothermic Verses Exothermic
Reactions
First notice the root of the word, Thermic
meaning heat or energy
 Next, look at prefix:

– Endo – In
– Exo - Out
Therefore
Endothermic refers to any change in
matter in which energy is absorbed
 Exothermic refers to any change in matter
in which energy is released

Measuring Heat Energy
The English measurement for measuring
energy is the calorie – the amount of thermal
energy needed to raise the temperature of
1.0 grams of water by 1C.
 The SI unit for measuring all energy
transfers is joules (N.m), abbreviated as J
 4.18 joules = 1.0 calories
67.3
 Examples:
16.1 calories = ______
joules
13.5

56.3 J = ________
calories

Temperature verses Heat
Temperature and heat are not synonyms.
 Heat is the transfer of energy between
objects that are at different temperatures
from the object with the higher temperature
to the object with the lower temperature.
 Temperature is the measure of how “hot” or
“cold” something is.
 More specifically, temperature is the average
kinetic energy of the particles in an object.

Temperature verses Heat
Temperature is an intensive property –
does not depend on the amount of the
substance.
 Heat is an extensive property – the energy
that can be transferred depends on the
amount of a substance one has.
 In other words, a pitcher and glass can be
filled with water at the same temperature,
but the pitcher of water can transfer more
energy.

How do we measure temperature?

We use different degrees
– Celsius
– Fahrenheit
– Kelvin
How do we change one into the
other? Formulas
F = 9/5 C + 32
 C = 5/9 (F – 32)

K = C + 273
 C = K – 273

Will be used
the most
F = 9/5 K – 459.4
 K = 5/9 (F + 459.4)

Practice
Convert
 Convert
 Convert
 Convert
 Convert
 Convert

61 C to F
64.4 F to C
452 C to K
698 K to C
698 F to K
1054 K to F
141.8 F
18 C
725.15 K
424.85 C
643.15 K
1437.53 F