Chapter 2Matter and Energy

Section 1: Energy

Section 2: Studying Matter and Energy

Section 3: Measurements and Calculations in Chemistry

Section 2.1 – Energy

OBJECTIVES:Explain that physical and chemical changes in matter involve

transfers of energyApply the law of conservation of energy to analyze changes in matter.

Distinguish between heat and temperature.

Convert between the Celsius and Kelvin temperature scales.

Energy and Change

• Energy is the capacity to do some kind of work.Such as:

- moving an object- forming a new compound- generating light

** No matter how energy is defined, it is always involved when there is a change in matter.

Changes in Matter can be Physical or Chemical

Physical Change:

A change of matter from one form to another without a change in chemical properties.

Chemical Change:

A change that occurs when one or more substances change into entirely new substances with different properties.

Every Change in Matter Involves a Change in Energy

Example: Energy is absorbed when a substance changes from a liquid to a gas.

Evaporation

The change of a substance from a liquid to a gas.

These physical changes require an input of energy.

Example: Energy is released when a substance changes from a gas to a liquid or when a liquid turns to a solid.

When ice freezes….. turns from a liquid to a solid, energy is released.

Endothermic and Exothermic Processes

Endothermic: Any change in matter in which energy is absorbed.Example: The melting of ice

The boiling of water

Exothermic: Any change in matter in which energy is released.Example: The freezing of water

The condensation of water vapor

Law of Conservation of Energy

Energy cannot be created or destroyed but can be changed from one form to another

Notice that the energy of the system increases while the energy of the surroundings decreases, however, the total energy remains

the same.

Energy is Often Transferred

The reaction between barium hydroxide and ammonium nitrate absorbs energy and causes ice crystals to form on the beaker.

To keep track of energy changes, chemists use the terms system and surroundings.

A system consists of all the components that are being studied at any given time.

In our example: the system is the mixture inside the beaker.

A surroundings include everything outside the system.

In our example: the surroundings consist of everything else including the air both inside and outside the beaker and the beaker itself.

Exothermic: Energy of the system surroundings

Endothermic: Energy of the surroundings system

HeatHeat is the energy transferred between objects that are at

different temperatures.

Heat energy is transferred from a warmer object to a cooler object.

heat

Kinetic EnergyKinetic Energy is the energy of an object that is due to the

object’s motion.

COLDHOT

Temperature

Temperature indicates how hot or cold something is.

Temperature is actually a measurement of the average kinetic energy of the random motion of particles in a

substance.

Temperature ScalesThe SI unit of temperature is the Kelvin (K)

Celsius Scale Kelvin ScaleFreezing point of water: 0° C Freezing point of water: 273 KBoiling point of water: 100° C Boiling point of water: 373 K

Lowest point: - 273° C Lowest point: 0 KThe Kelvin scale measures the kinetic energy of the particles

in the object.** It is not possible to have negative kinetic energy.

Conversions:°C = K – 273 K = °C + 273

°F = (°C x 9/5) + 32 °C = (°F – 32) x 5/9

Transfer of Heat May Not Affect the TemperatureThe transfer of energy as heat does not always result in a

change of temperature.

Heat of Fusion: The heat energy required to change a solid to a liquid

Heat of Vaporization: The heat energy required to change a liquid to a gas.

Specific Heat

The relationship between energy transferred as heat to a substance and the substance’s temperature change is called

Specific Heat

Definition: The quantity of heat required to raise a unit mass of homogeneous material 1 K or 1°C in a specified way given constant pressure and volume.

Restated: The specific heat of a substance is the quantity of energy as heat that must be transferred to raise the temperature of 1 gram of a substance 1 K.

Specific heat is measured in joules per gam kelvin (J/g·K)

Section 2.2 – Studying Matter and Energy

OBJECTIVES:Describe how chemists use the scientific method

Explain the purpose of controlling the conditions of an experiment.

Explain the difference between a hypothesis, a theory, and a law.

Scientific Method

Ask a question Form a hypothesis

Hypothesis: a theory or explanation that is bases on observations and that can be tested

Test the hypothesis Analyze the results Draw conclusions Revise and retest the hypothesis

Or Construct a theory

Theory: a well tested explanation of observations, experimentation, and reasoning

A law is a summary of many experimental results and observations; a law tells how things work.

Law of Conservation of Mass

Mass cannot be created or destroyed in ordinary chemical and physical changes.

Section 2.3Measurements and Calculations in

Chemistry

OBJECTIVES:Distinguish between accuracy and precision in measurements.

Determine the number of significant figures in a measurement, and apply rules for significant figures in calculations.

Calculate changes in energy using the equation for specific heat, and round the results to the correct number of significant figures.

Write very large and very small numbers in scientific notation.

Accuracy: How close the measurement is to the true or actual value.

Precision: The exactness of a measurement. (How closely several measurements of the same quantity made in the same way agree with one another)

Significant Figures

The significant figures of a measurement or a calculation consist of all the digits known with

certainty as well as one estimated, or uncertain, digit.

*** Print off table with significant figure measurements – graduated cylinders

Rules for Determining Significant Figures

Non-zero digits are always significantEx. 12.4 has 3 significant figures6.295 has 4 significant figures

Zeros between non-zero digits are significantEx. 40.71 has 4 significant figures87, 009 has 5 significant figures

Zeros in front of non-zero digits are not significantEx. 0.0095 has 2 significant figures

0.00005 has 1 significant figure

Zeros both at the end of a number and to the right of a decimal point are significantEx. 85.00 has 4 significant figures629.000 has 6 significant figures

Zeros both at the end of a number but to the left of a decimal point may not be significant. If a zero has not been measured or estimated, it is not significant. A decimal point

placed after zeros indicates that the zeros are significant.Ex. 2000 has 1 significant figure2000. has 4 significant figures

** Worksheet – significant figures #1

Performing Calculations using Significant Figures

Adding and Subtracting:The result must be rounded to the same place as the least precise

measurement.

Ex. 1.31 + 0.615 = 1.925** Since 1.31 only goes to the hundredth place…we have to round the answer.

The answer should be 1.93.

Multiplying and Dividing:

The result must have the same number of significant figures as the least precise number.

Ex. 13 x 25.0 = 325.0** Since 13 is 2 significant figures….325.0 must be rounded to 2 sig. figs.The answer should be 330 330 has only 2 sig figs…the zero is a place holder.

** Worksheet – significant figures #2

Rounding Rule:To round a number:

Leave the last significant digit unchanged if the next digit is 4 or less

add 1 to it if the next digit is 5 or more

Ex. Round to the tenths place1.035 rounds to 1.0675.25 rounds to 675.3831.478 rounds to 831.5

Scientific Notation

Scientific Notation is used to express very small or very large numbers.Scientific Notation requires one digit to the left of the decimal point and is expressed using powers of 10.

Example: 3.86 x 103 = 3,8602.752 x 10-4 = .0002752

The following are NOT in scientific notation:62.854 x 106

0.962 x 10-4

Putting a number into scientific notation from standard decimal

Rule 1: If moving the decimal to the left, add to the exponent the number of places that the decimal was moved.

Example A:

3476.29 scientific notation

3.47629 x 103 Note: the decimal was moved three places to the left

Example B:

48.145 x 105 scientific notation

4.8145 x 106 Note: the decimal was moved one place to the left, therefore, we added one to the existing exponent

Rule 2: If moving the decimal to the right, subtract from the exponent the number of places that the decimal was moved.

Example A:

.00329 scientific notation

3.29 x 10-3 Note: the decimal was moved three places to the right

Example B:

.00014568 x 105 scientific notation

1.4568 x 101 Note: the decimal was moved four places to the right, therefore, we added four to the existing exponent

Putting a number from scientific notation to standard decimal

Rule 1: If there is a positive exponent, move the decimal to the right. Add zeros for place holders where necessary.

Example A:

6.459 x 104 standard decimal

64,590 Note: the decimal was moved four places to the right. Notice that a zero was added on the right as a place holder.

Rule 2: If there is a negative exponent, move the decimal to the left. Add zeros for place holders where necessary.

Example B:

3.812 x 10-3 standard decimal

.003812 Note: the decimal was moved three places to the left. Notice that zeros were added on the left as place holders.

Multiplying numbers in scientific notation

(4.632 x 103) (2.8964 x 105) = 13.4161248 x 108

Display the answer in correct Scientific Notation

1.34161248 x 109

(9.11 x 103) (6.896 x 10-5) = 62.82256 x 10-2

Display the answer in correct Scientific Notation

6.282256 x 10-1

Dividing numbers in scientific notation

(1.142371296 x 108) / (2.64 x 102) = .4327164 x 106

Display the answer in correct Scientific Notation

4.327164 x 105

(2.08266096 x 103) / (6.896 x 10-5) = 0.30201 x 108

Display the answer in correct Scientific Notation

3.0201 x 107

Specific Heat

Definition: The quantity of heat required to raise a unit mass of homogeneous material 1 K or 1°C in a specified

way given constant pressure and volume.

cp = q m x ΔT

cp = specific heat at constant pressureq = heat energy

m = massΔT = change in temperature

Element Specific Heat (J/g · K)Aluminum 0.897Cadmium 0.232Calcium 0.647Carbon 0.709

Chromium 0.449Copper 0.385

Gold 0.129Iron 0.449Lead 0.129Neon 1.030Nickel 0.444

Platinum 0.133Silicon 0.705Silver 0.235Water 4.18Zinc 0.388

Assignments

Section 2.1 Pg 45 #1-8, 11-13Lab

Worksheet #1 Significant FiguresWorksheet #2 Significant Figures

QUIZ – Significant Figures, 2.1Section 2.3 (Specific Heat) Pg 61 # 1-4

Worksheet #3 Scientific NotationSection 2.3 Pg 63 # 1—9

QUIZ – Significant Figures and Scientific NotationTEST – Chapter 2