Properties of Matter Chapter 4 Hein and Arena Eugene Passer Chemistry Department Bronx Community College © John Wiley and Sons, Inc Version 2.0 12th Edition

Chapter Outline 4.1 Properties of Substances 4.6 Heat: Quantitative Measurement 4.2 Physical Changes 4.7 Energy in Chemical Changes 4.3 Chemical Changes 4.8 Conservation of Energy 4.4 Conservation of Mass 4.5 Energy

4.1 Properties of Substances

Properties of a Substance A property is a characteristic of a substance. Each substance has a set of properties that are characteristic of that substance and give it a unique identity.

Physical Properties

The inherent characteristics of a substance that are determined without changing its composition. Examples: taste color physical state melting point boiling point

Physical Properties of Chlorine 2.4 times heavier than air color is yellowish-green odor is disagreeable melting point –101oC boiling point –34.6oC

Chemical Properties

Describe the ability of a substance to form new substances, either by reaction with other substances or by decomposition.

Chemical Properties of Chlorine It will not burn in oxygen. It will support the combustion of certain other substances. It can be used as a bleaching agent. It can be used as a water disinfectant. It can combine with sodium to form sodium chloride.

4.2 Physical Changes

Physical Changes Changes in physical properties (such as size, shape, and density) or changes in the state of matter without an accompanying change in composition. Examples: tearing of paper change of ice into water change of water into steam heating platinum wire No new substances are formed.

4.3 Chemical Changes

In a chemical change new substances are formed that have different properties and composition from the original material.

Formation of Copper(II) Oxide Heating a copper wire in a Bunsen burner causes the copper to lose its original appearance and become a black material. The formation of copper(II) oxide from copper and oxygen is a chemical change. The copper (II) oxide is a new substance with properties that are different from copper. The black material is a new substance called copper(II) oxide. Copper is 100% copper by mass. Copper (II) oxide is: 79.94% copper by mass 20.1% oxygen by mass. Heating a copper wire in a Bunsen burner causes the copper to lose its original appearance and become a black material.

Formation of Copper(II) Oxide Neither Cu nor O2 contains Cu2+ or O2- A chemical change has occurred. Copper(II) oxide is made up of Cu2+ and O2- 4.2

Decomposition of Water But the burning splint is extinguished when placed into the water sample. They are both colorless gases. The composition and physical appearance of hydrogen and oxygen are different from water. Water is decomposed into hydrogen and oxygen by passing electricity through it. The hydrogen explodes with a pop upon the addition of a burning splint. The oxygen causes the flame of a burning splint to intensify.

Chemical Equations

Water decomposes into hydrogen and oxygen when electrolyzed. reactant products yields

Chemical symbols can be used to express chemical reactions

Water decomposes into hydrogen and oxygen when electrolyzed. reactant products 2H2O 2H2 O2 yields

Copper plus oxygen yields copper(II) oxide. heat reactants product yield

2Cu O2 2Cu2O Copper plus oxygen yields copper(II) oxide. heat product reactants product 2Cu O2 2Cu2O yield

4.4 Conservation of Mass

No change is observed in the total mass of the substances involved in a chemical change.

sodium + sulfur  sodium sulfide → 46.0 g 32.1 g 78.1 g 78.1 g reactant 78.1 g product mass reactants = mass products

4.5 Energy

Energy is the capacity to do work

Types of Energy mechanical chemical electrical heat nuclear radiant

Energy that an object possesses due to its relative position. Potential Energy Energy that an object possesses due to its relative position.

The potential energy of the ball increases with increasing height. increasing potential energy 50 ft increasing potential energy 20 ft

Potential Energy Stored energy

Gasoline is a source of chemical potential energy. The heat released when gasoline burns is associated with a decrease in its chemical potential energy. The new substances formed by burning have less chemical potential energy than the gasoline and oxygen.

Energy matter possesses due to its motion. Kinetic Energy Energy matter possesses due to its motion.

Moving bodies possess kinetic energy. The flag waving in the wind.

Moving bodies possess kinetic energy. A bouncing ball. The running man.

Moving bodies possess kinetic energy. The runner

Moving bodies possess kinetic energy. The soccer player.

4.6 Heat: Quantitative Measurement

A form of energy associated with small particles of matter. Heat A measure of the intensity of heat, or of how hot or cold a system is. Temperature

Units of Heat Energy

(exactly) 4.184 Joules = 1 calorie The SI unit for heat energy is the joule (pronounced “jool”). Another unit is the calorie. 4.184 J = 1 cal (exactly) 4.184 Joules = 1 calorie This amount of heat energy will raise the temperature of 1 gram of water 1oC.

An Example of the Difference Between Heat and Temperature A form of energy associated with small particles of matter. A measure of the intensity of heat, or of how hot or cold a system is.

A B 100 g water 20oC 100 g water 30oC 200 g water 200 g water 20oC Twice as much heat energy is required to raise the temperature of 200 g of water 10oC as compared to 100 g of water. 4184 J 8368 J temperature rises 10oC heat beakers

Specific Heat

The specific heat of a substance is the quantity of heat required to change the temperature of 1 g of that substance by 1oC.

The units of specific heat in joules are:

The units of specific heat in calories are:

The relation of mass, specific heat, temperature change (Δt), and quantity of heat lost or gained is expressed by the general equation: Δt = heat mass of substance ) ( specific heat of substance

Example 1

Calculate the specific heat of a solid in J/goC and in cal/ goC if 1638 J raise the temperature of 125 g of the solid from 25.0oC to 52.6oC. (mass of substance)(specific heat of substance)Δt = heat (g)(specific heat of substance)Δt = heat heat = 1638 J mass = 125 g Δt = 52.6oC – 25.0oC = 27.6oC

Calculate the specific heat of a solid in J/goC and in cal/ goC if 1638 J raise the temperature of 125 g of the solid from 25.0oC to 52.6oC. Convert joules to calories using 1.000 cal/4.184 J

Example 2

A sample of a metal with a mass of 212 g is heated to 125 A sample of a metal with a mass of 212 g is heated to 125.0oC and then dropped into 375 g of water at 240.0oC. If the final temperature of the water is 34.2oC, what is the specific heat of the metal? When the metal enters the water, it begins to cool, losing heat to the water. At the same time, the temperature of the water rises. This process continues until the temperature of the metal and the temperature of the water are equal, at which point (34.2oC) no net flow of heat occurs.

A sample of a metal with a mass of 212 g is heated to 125 A sample of a metal with a mass of 212 g is heated to 125.0oC and then dropped into 375 g of water at 240.0oC. If the final temperature of the water is 34.2oC, what is the specific heat of the metal? Calculate the heat gained by the water. Calculate the final temperature of the metal. Calculate the specific heat of the metal.

Heat Gained by the Water A sample of a metal with a mass of 212 g is heated to 125.0oC and then dropped into 375 g of water at 240.0oC. If the final temperature of the water is 34.2oC, what is the specific heat of the metal? Heat Gained by the Water temperature rise of the water Δt = 34.2oC – 24.0oC = 10.2oC heat gained by the water =

A sample of a metal with a mass of 212 g is heated to 125 A sample of a metal with a mass of 212 g is heated to 125.0oC and then dropped into 375 g of water at 240.0oC. If the final temperature of the water is 34.2oC, what is the specific heat of the metal? Heat Lost by the Metal Once the metal is dropped into the water, its temperature will drop until it reaches the same temperature as the water (34.2oC). temperature drop of the metal Δt = 125.0oC – 34.2oC = 90.8oC heat lost by the metal heat gained by the water = =

A sample of a metal with a mass of 212 g is heated to 125 A sample of a metal with a mass of 212 g is heated to 125.0oC and then dropped into 375 g of water at 240.0oC. If the final temperature of the water is 34.2oC, what is the specific heat of the metal? The heat lost or gained by the system is given by: (mass) (specific heat) (Δt) = energy change rearrange specific heat of the metal =

4.7 Energy in Chemical Changes

In all chemical changes, matter either absorbs or releases energy.

Energy Release From Chemical Sources Type of Energy Energy Source Electrical Storage batteries Light A lightstick. Fuel combustion. Heat and Light Combustion of fuels. Body Chemical changes occurring within body cells.

Chemical Changes Caused by Absorption of Energy Type of Energy Chemical Change Electrical Electroplating of metals. Decomposition of water into hydrogen and oxygen Light Photosynthesis in green plants.

4.8 Conservation of Energy

An energy transformation occurs whenever a chemical change occurs. If energy is absorbed during a chemical change, the products will have more chemical potential energy than the reactants. If energy is given off in a chemical change, the products will have less chemical potential energy than the reactants.

H2 + O2 have higher potential energy than H2O energy is absorbed energy is given off lower potential energy Electrolysis of Water Burning of Hydrogen in Air 4.3

Law of Conservation of Energy Energy can be neither created nor destroyed, though it can be transformed from one form of energy to another form of energy.

The End