CHEM 10 CHP 3

transcript

CHEM 10 CHP 3

MATTER & ENERGY

Matter

• Anything that occupies space and has mass

• Composed ultimately of atoms

Structure Determines Properties

• the atoms or molecules have different structures in solids, liquid and gases, leading to different properties

Classifying Physical States of Matter:

Solid: it has a definite shape and volume

Liquid: it has a definite volume, but no shape; takes on shape of container

Gas: it has no definite shape and no definite volume (fills shape of container, but mostly empty space)

TYPES OF SOLIDS

Crystalline: regular repeated patterns Salt, sugar, quartz

Amorphous: no patterns Plastic, gel, glass

Substances and Mixtures

Substance - matter with a definite , fixed compositionAlso known as pure substancesExamples - elements or compounds

Mixture – two or more substances that mix, homogeneous or heterogeneousExamples – coffee or cereal

See Figure 3.8: memorize!

Classifying Matter

Substances and Mixtures: DefinitionsHomogenous - uniform appearance - has

same properties throughout, like coffeeHeterogeneous - contains two or more

physically distinct phases, like ice cubes in water or oil on top of water

Phase - homogeneous part of system - separated by boundaries

System - body of matter under consideration

Elements

Fundamental/elementary substances that cannot be broken down by chemical means into simpler substances

Atom is the smallest particle of an element

91 elements occur naturally in nature

Compounds

Made of two or more elements with some type of bonding arrangement

Examples: water H2O

ethanol CH3CH2OH

sugar (sucrose) C12H22O11

table salt NaCl

ELEMENTS & COMPOUNDS

Element names and symbols:- Elements are made of atoms or

diatomic molecules- Compounds are made of atoms

from two different elements, which form molecules or formula units

ELEMENTS & COMPOUNDS

Examples:

Au is symbol for atom of gold, pure element

Learn all the seven diatomic gases.H2 is symbol for a diatomic molecule for pure

element hydrogen

H2O consists of a molecule that has two hydrogen atoms and 1 oxygen atom

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:tastecolorphysical statemelting pointboiling point

(from another textbook)

Chemical Properties

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

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.

Chemical Properties of Chlorine

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 paperchange of ice into waterchange of water into steamheating platinum wire

No new substances are formed.

Chemical Changes

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

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

Heating a copper wire in a Bunsen burner causes the copper to lose its original appearance and become a black material.

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.

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.

Formation of Copper(II) Oxide

Copper(II) oxide is made up of Cu2+ and O2-

Neither Cu nor O2 contains Cu2+ or O2-A chemical change has occurred.

Water is decomposed into hydrogen and oxygen by passing electricity through it.

Decomposition of Water

The composition and physical appearance of hydrogen and oxygen are different from water.The hydrogen explodes with a pop upon the addition of a burning splint.The oxygen causes the flame of a burning splint to intensify.

They are both colorless gases.But the burning splint is extinguished when placed into the water sample.

Water decomposes into hydrogen and oxygen when electrolyzed.

reactant productsyields

CHEMICAL EQUATIONS

Water decomposes into hydrogen and oxygen when electrolyzed.

reactant yields

2H2O 2H2 O2

products

Copper plus oxygen yields copper(II) oxide.

yield productreactants

Copper plus oxygen yields copper(II) oxide.

yield productreactants

2Cu O2 2CuO

Law of Conservation of Mass

Antoine Lavoisier

“Matter is neither created nor destroyed in a chemical reaction”

The total amount of matter present before a chemical reaction is always the same as the total amount after

The total mass of all the reactants is equal to the total mass of all the products

sodium + sulfur sodium sulfide

46.0 g 32.1 g 78.1 g

78.1 g product

mass productsmass products

78.1 g reactant →

mass reactantsmass reactants ==

ENERGY!!!!

• Energy is the capacity to do work• Two main forms of energy:

• Potential• Nonpotential

Potential Energy

Energy that an object possesses due to its relative position.

Stored energy: positional, chemical, etc.

increasing potential energy

The potential energy of the ball increases with increasing height.

increasing 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.

• Gasoline is a source of chemical potential energy.

Types of Nonpotential EnergyMechanical/kinetic: Energy matter possesses due to its

motion. KE = ½ mv2

Chemical: produced in reactions; potential energy in the attachment of atoms or because of their position

Electrical: kinetic energy associated with the flow of electrical charge

Heat or thermal: q = m * cp *TNuclear: potential energy in the nucleus of atoms Radiant or Light: E = h

Moving bodies possess kinetic energy.

• A bouncing ball.• The running man.

Heat• A form of energy associated with

small particles of matter.

Temperature • A measure of the intensity of heat, or of how hot or cold a system is.

Heat: Heat: Quantitative MeasurementQuantitative Measurement

• 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.

Twice as much heat energy is required to raise the temperature of 200 g of water 10oC as compared to 100 g of water.

200 g water

100 g water

200 g water

heat beakers 4184 J 8368 Jtemperaturerises 10oC

The specific heat (capacity), cp, 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:

Joulesgram Celcius

The units of specific heat in calories are: o

caloriesgram Celcius

calg C

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

ΔT = heatmass of substance)(specific heat

of substance)(q = m*cp*T MEMORIZE THIS!!

1638 J125 g x 27.6 C

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)(specific heat)ΔT = q

(m)(cp)ΔT = qq = 1638 J

m = 125 g

ΔT = 52.6oC – 25.0oC = 27.6oC

0.475 J=

cp = q/mT

(0.114 cal/goC)

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 24.0oC. 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.

• Calculate the heat gained by the water.

• Calculate the final temperature of the metal.

• Calculate the specific heat of the metal.

ΔT = 34.2oC – 24.0oC = 10.2oCtemperature rise of the water

Heat Gained by the Water

o(10.2 C) = (375 )g o

4.184 Jg C

heat gained by the water

= 41.60 x 10 J

ΔT = 125.0oC – 34.2oC = 90.8oCtemperature drop of 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).

Heat Lost by the Metal

heat lost by the metal

heat gained by the water

= = 41.60 x 10 J

1.60 x 10 J(212g)(90.8 C)

0.831 Jg C)

The heat lost or gained by the system is given by:

(m) (cp) (ΔT) = q

An energy transformation occurswhenever 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.

Conservation of Conservation of EnergyEnergy

H2 + O2 have higher potential energy than H2O

energy is given offenergy is absorbed

Electrolysis of Water

(endothermic)

Burning of Hydrogen in Air

(exothermic)

higher potential energy lower potential energy

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.

CHEM 10 CHP 3

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