Transcript Matter and Energy

Matter and Energy
Chapter 2
Chemistry 1 5.0
Energy and Change
Energy is the capacity to do work.
 All physical and chemical changes require
energy.
 Endothermic - describes a process in
which heat is absorbed from the
environment.
 Exothermic – describes a process in which
heat is released into the environment.

Law of Conservation of Energy

Energy is neither created, nor destroyed.
It just changes forms.
Heat

Heat is the energy transferred between objects
that are at different temperatures. This heat is
always transferred from the hotter object to the
colder object.

Types of Energy
Potential energy – stored energy
Kinetic energy – energy of motion
Heat

Temperature is not the same as heat.

Temperature is a measure of the average
kinetic energy of the particles in an object.
A temperature change is a result of a
energy transfer.
 Temperature vs. Heat Animation

TEMPERATURE SCALES

Celsius and Kelvin Temps.
= °C + 273

K

°C = K - 273

Zero Point on Kelvin Scale – Absolute Zero
0

K and -273 °C
All motion of particles stops! No kinetic
energy.
Heat Transfer

Transfer of heat may not affect
temperature.

During a phase change, the temperature
will remain constant until all of the
substance has changed state.

The temperature will increase when a
substance is a solid, liquid, or gas.
Phase Change Diagram
Kinetic Theory of Matter

Gases posses the greatest amount of kinetic
energy.

Two factors that determine the state of matter of
a substance: speed of particles and distance

There are two factors contribute to the
attraction between the particles.
Kinetic Theory of Matter

Substances change phases when they
overcome these attractions.

The overall kinetic energy will not change until
the entire substance has completely changed.

Comparison of the three states of matter
Specific Heat

The amount of heat necessary to raise 1g
of a substance 1°C. This is the
relationship between energy transferred as
heat and the substances temperature
change.

Common Specific Heats
The scientific method is a
systematic approach to gather
knowledge.
Observation
 Question
 Hypothesis
 Experiment
 Conclusion


All hypotheses must be able to be
tested in order to be a true hypothesis.
Experiment

Natural Law – Describes how nature
behaves

Theory – Explains why nature behaves
the way it does
A theory and a hypothesis are both
explanations, but a theory is an
explanation formed after much
experimentation.
Variables in a Experiment

Independent Variable - You control

Dependent Variable – Variable factor –
what is being tested

Experimental Control – Factor that
remains constant for comparison
D. Factors in an Experiment
Independent: most regular variable – goes on the X-axis
2. Dependent: what you are testing – goes on the Y-axis
3. Experimental Control: part of the experiment that stays
the same.
1.
Dependent variable
“Y” axis
Independent variable
“X” axis
Uncertainty in Measurement
Measurements are uncertain because:
 1) Instruments are not free from error.
 2) Measuring involves some estimation.
 Precision –when the instrument gives you
about the same results under similar
conditions. The smaller the increments of
measurement an instrument has, the more
precise it can be.
 Accuracy – when the experimental value is
close to the actual value.

What is the goal for a game of darts?
Hitting the Bulls Eye!
Label the following data as
accurate, precise, neither, or both.
1) 200g, 1g, 40g
 Neither

2) 78g, 80g, 79g
 Precise

3) 16g, 14g, 17g
 Accurate and Precise

Significant Figures and Digits

A prescribed decimal that determines the
amount of rounding off to be done base on
the precision of the experiment.

ALWAYS ESTIMATE 1 DIGIT MORE
THAN THE INSTRUMENT MEASURES.

Significant digits include measured digits
and the estimated digit.
VI. Significant Digits
A. Significant Digits include measured digits and
estimated digits.
 Use Atlantic-Pacific Rule – imagine a US map

decimal
decimal
point
point
Pacific
Atlantic
1100
1100.
2 significant digits
4 significant digits
11.010000
8 significant digits
2 significant digits
0.025
0.00035000
1,000,100
Decimal
Present
Start
counting
with the 1st
nonzero
digit and
count all
the rest.
5 significant digits
5 significant digits
Decimal
Absent
Start
counting
with the 1st
nonzero
digit and
count all
the rest.
How to use a
graduated cylinder
Read the
meniscus
How to use a graduated cylinder
36.4 mL
19.0 mL
6.25 mL
How to read a triple beam balance
28.570 g
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
How to read a triple beam balance
109.076 g
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
Significant Digits in Addition and
Subtraction

Add or subtract numbers

Answer can only be as exact as the least
exact number. (Look at the decimal place)

Ex. 4.1 cm + 0.07cm

4.17 cm
Significant Digits and Multiplication
and Division

Multiply and Divide the numbers.

Round answer to the same number of
significant digits as the number with the fewest
significant digits.
Ex. 7.079 cm / 0.535 cm
 13.2317757
 13.2

Scientific Notation
1) 2700
2.7 x 103
2) 8,000,000
8 x 106
3) 0.0035
3.5 x 10-3
4) 0.010
1.0 x 10-2
1st Commandment of Chemistry: KNOW THY CALCULATOR!
Find the “EE” key – it may
be a 2nd function!
If you have a
graphing
calculator look
for the following
keys:
Find the (-) key.
Find the “Exp” or “x10x”
1st Law of Chemistry:
Know Thy Calculator!
Look at the
calculator that is
similar to
yours…
Find the “(-)” or the
“+/-” key.
Scientific Notation

1) Multiply 3.7 x 102 by 5.1 x 103

Answer: 19 x 105

2) Divide 2.3 x 10-3 by 4.6 x 10-6

Answer: 5.0 x 102
Scientific Notation

Add 9.67x102 + 8.5x103

Answer: 9.5 x 103