TABLE OF CONTENTS - Chapter 1: Basic Concepts of Chemistry © 2024 ...

Solution and Answer Guide: Kotz Treichel Townsend Treichel, Chemistry and Chemical Reactivity 11e, 978-0-357-85140-1,

Chapter 1: Basic Concepts of Chemistry

1 © 2024 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.Solution and Answer Guide Kotz Treichel Townsend Treichel, Chemistry and Chemical Reactivity 11e, 978-0-357-85140-1,

Chapter 1: Basic Concepts of Chemistry

TABLE OF CONTENTS

Think–Pair–Share ....................................................................................................................................... 2

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Solution and Answer Guide: Kotz Treichel Townsend Treichel, Chemistry and Chemical Reactivity 11e, 978-0-357-85140-1,

Chapter 1: Basic Concepts of Chemistry

2 © 2024 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

THINK–PAIR–SHARE

• Hypotheses, Laws, and Theories
• What are the differences between a hypothesis and a theory?
• Why is the law of constant composition a law and not a theory?

Answer:

a. Differences between a hypothesis and a theory:

An hypothesis is an initial supposition regarding a data set, observable phenomenon, or circumstance that one encounters. Typically, hypotheses are based upon a small data set and are initially ill-formed. Hypotheses are tentative explanations or predictions of observations. Theories, on the other hand, are much more complete explanations of phenomena. Theories are well-tested, unifying principles that explain a body of facts and any related laws. Theories are constantly under scrutiny to see if they do or do not explain newly discovered phenomenon.

b. Law of constant composition:

Theories are constructs designed to explain phenomena. They are frequently reexamined to determine if they sufficiently explain new results. Scientific laws are explanations that always yield the same result. The law of constant composition states that a given chemical compound is always composed of the same elements in a specific ratio. For example, carbon dioxide, CO2, is composed of one carbon atom and two oxygen atoms. There are no carbon dioxide molecules having different elements or different ratios of carbon and oxygen.

• Carbon dioxide consists of molecules containing one carbon atom and two oxygen atoms. In each molecule

the three atoms are arranged in a line with the carbon in between the two oxygen atoms. Make a drawing, based on the kinetic-molecular theory, of the arrangement of carbon dioxide molecules in (a) the solid state, (b) the liquid state, and (c) the gas state. In your drawing, represent the carbon atoms with a solid circle and the oxygen atoms with an open circle. For each case, draw 10 molecules. It is acceptable for your diagram to be two dimensional.

Answer:

Carbon dioxide drawings:

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Solution and Answer Guide: Kotz Treichel Townsend Treichel, Chemistry and Chemical Reactivity 11e, 978-0-357-85140-1,

Chapter 1: Basic Concepts of Chemistry

3 © 2024 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

• Some students come to a chemistry class thinking that all samples of elements consist of isolated atoms and

all samples of compounds consist of molecules.

• Are all elements found in nature as isolated atoms? If not, how else can the atoms be arranged?
• Are all compounds composed of molecules? If not, what other types of particles are found in some

compounds?

• Is N2 an element or a compound? Explain your answer.

Answer:

a. Elements found in nature as isolated atoms:

All elements are not found in nature as isolated atoms. Some elements are indeed isolated atoms such as the noble gases He, Ne, Ar, Kr, Xe, and Rn. Other elements are aggregations of isolated atoms like gold, copper, sodium, and several other metallic elements. But many other elements in their elemental forms are composed of molecules. For example, elemental nitrogen, oxygen, and fluorine are diatomic molecules N2, O2, and F2. Phosphorus is a tetratomic molecule, P4, and sulfur has several molecular forms including the octaatomic molecule S8.

b. Compounds composed of molecules:

Many compounds are molecules including water, H2O, carbon dioxide, CO2, and methane, CH4, as examples. However not all compounds are molecules. Table salt, NaCl, is an ionic compound composed of sodium ions, Na + , and chloride ions, Cl – . There are numerous other examples of ionic compounds including magnesium oxide, MgO, aluminum chloride, AlCl3, and potassium sulfide, K2S. Some compounds are composed of both ions and molecules. For example, sodium phosphate, Na3PO4, is composed of Na + ions and PO4 3– ions but the PO4 3– units are an ionic molecule, a molecule that is charged.

c. N2 an element or a compound:

N2 is an element not a compound. To be a compound more than one element held together by chemical bonds is necessary.

• Answer the following.
• Zinc is a shiny silver-colored solid that reacts vigorously with hydrochloric acid. Identify each of

these properties as being either a physical property or a chemical property. Explain your reasoning.

• The mass of a piece of aluminum is 10.0 g, its volume is 3.70 cm

3 , and its density is 2.70 g/cm 3 .Identify each of these properties as being either an intensive property or an extensive property.Explain your reasoning.

• Identify each of the following as being either a physical change or a chemical change. Explain

your reasoning.

• Bubbles of carbon dioxide gas form when baking soda is added to vinegar.

ii. Paper burns. 3 / 4

Solution and Answer Guide: Kotz Treichel Townsend Treichel, Chemistry and Chemical Reactivity 11e, 978-0-357-85140-1,

Chapter 1: Basic Concepts of Chemistry

4 © 2024 Cengage Learning, Inc. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.iii. Sugar dissolves in water.iv. Water boils.

Answer:

Physical, chemical, intensive and extensive properties of zinc and aluminum:

• Shiny silver-color is a physical property. Reaction of zinc with hydrochloric acid a chemical

property. Color of a substance is determined without altering its composition. Zinc and hydrochloric acids’ composition is changed after their reaction indicating a chemical property.

• Mass and volume are extensive properties. Both change depending upon the amount of substance

present. Density is an intensive property. The density of aluminum is the same whether you have 10 g, 100 g, or 1000 g of aluminum.

c. Identify physical or chemical changes:

• Bubbles of carbon dioxide gas form when baking soda is added to vinegar.

Chemical property – baking soda is chemically altered upon reaction with vinegar.ii. Paper burns.Chemical property – paper is no longer paper once it’s burned. It has become primarily charred carbon.iii. Sugar dissolves in water.Physical property – We can recover the sugar, in its same form, by evaporating the water.iv. Water boils.Physical property – Water in the liquid state or the gaseous state is still water.

• Give one or more examples of each of the following types of energy conversions.
• Chemical potential energy into electrical energy.
• Chemical potential energy into thermal energy.
• Thermal energy into mechanical energy.
• Chemical potential energy into sound and/or light energy.

Answer:

Energy conversion examples:

• Chemical potential energy into electrical energy

Combustion of fuels like coal and natural gas at electrical power plants to produce electricity.

• Chemical potential energy into thermal energy

Fuel combustion in a fireplace, BBQ grill, furnace, etc.

• Thermal energy into mechanical energy

Internal combustion engines like those found in cars and motorcycles as well as steam engines turn heat into mechanical energy.

• Chemical potential energy into sound and/or light energy

Any explosion involving combustion of chemicals turns chemical potential energy into sound and/or light. Examples include bullets in guns, dynamite, artillery shells, and nitroglycerin explosions.

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