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 EnergyPotential energy – stored energyKinetic 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. K = °C + 273

°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 doesA 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

1. Independent: most regular variable – goes on the X-axis2. Dependent: what you are testing – goes on the Y-axis3. Experimental Control: part of the experiment that stays

the same.

Independent variable

“X” axis

Dependent variable

“Y” 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

Atlantic

Pacific

decimal

point

decimal

point

1100

1100.

11.010000 0.025

0.00035000

2 significant digits4 significant digits8 significant digits2 significant digits5 significant digits

Decimal Absent Start counting with the 1st nonzero digit and count all the rest.

Decimal Present Start counting with the 1st nonzero digit and count all the rest.

1,000,100 5 significant digits

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

Ohaus Triple Beam Balance Tutorial

Reading A Triple Beam Balance Tutorial

28.570 g

How to read a triple beam balance

Ohaus Triple Beam Balance Tutorial

Reading A Triple Beam Balance Tutorial

109.076 g

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

4.2 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

2.7 x 103

8 x 106

1) 2700

2) 8,000,000

3) 0.0035 3.5 x 10-3

4) 0.010 1.0 x 10-2

Find the “EE” key – it may be a 2nd function!

Find the (-) key.If you have a graphing calculator look for the following keys:

1st Commandment of Chemistry: KNOW THY CALCULATOR!

Find the “Exp” or “x10x”

Find the “(-)” or the “+/-” key.

Look at the calculator

that is similar to yours…

1st Law of Chemistry:

Know Thy Calculator!

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