chemical change is a process that involves recombining atoms and energy flows

UNIT A: CHEMISTRY

Chemical change is a process that involves recombining atoms and energy flows.

In this unit, you will learn about...

General Outcome #3 – Identify and classify chemical changes, and write word and balanced chemical equations for significant chemical reactions, as applications of Lavoisier’s law for conservation of mass

○ ROCK – describe the evidence for chemical changes (energy change, formation of gas or precipitate, color or odour change, change in temperature)

○ ROCK – differentiate between endothermic and exothermic chemical reactions

○ ROCK – translate word equations to balanced chemical equations and vice versa for chemical reactions that occur in living and non living systems

○ ROCK – classify and identify categories of chemical reactions (formation, decomposition, hydrocarbon combustion, single replacement, double replacement)

○ ROCK – predict the products of formation (synthesis) and decomposition, single and double replacement and hydrocarbon combustion chemical reactions, when given the reactants

○ ROCK – interpret balanced chemical equations in terms of moles of chemical species and relate the mole concept to the law of conservation of mass

○ SAND – identify chemical reactions that are significant in societies

○ SAND – define the mole as the amount of an element containing 6.02 X 1023 atoms (Avogadro’s number) and apply the concept to calculate quantifies of substances of other chemical species

○ SAND – provide examples of household, commercial and industrial processes that use chemical reactions to produce useful substances and energy

The Ultimate Chemical Reaction

What do you think would be one of the coolest things to experience??

http://www.spaceflight.nasa.gov/gallery/video/shuttle/sts-112/qtime/sts112fd01a.mov

http://www.spaceflight.nasa.gov/gallery/video/shuttle/sts-112/qtime/sts112fd01a.mov

UNIT A: CHEMISTRY

A3.1: Important Examples of Chemical Change

In this section, you will learn about...


○ ROCK – describe the evidence for chemical changes (energy change, formation of gas or precipitate, color or odour change, change in temperature)

○ ROCK – differentiate between endothermic and exothermic chemical reactions

○ SAND – identify chemical reactions that are significant in societies

○ SAND – provide examples of household, commercial and industrial processes that use chemical reactions to produce useful substances and energy

Did you know??

Slicing an onion causes your eyes to sting because of a chemical reaction. Slicing ruptures the onion’s cells allowing substances to mix. A gas is produced and reacts with the water in your eyes – producing dilute sulfuric acid!

Important Examples of Chemical Change

When was the last time you watched an awesome display of fireworks? Fireworks is one example of chemical change (occurs when a substance or substances react in a chemical reaction to create a different substance or substances) occurring. Other examples of chemical change include dough rising, the changing taste of food cooking on a barbecue, the combustion of fuel in a motor vehicle, a glowing glow stick, and the changing temperature of a hot or cold pack.

Important Examples of Chemical Change

The substances that react are called reactants and the new substances that are produced are called products

The products have completely different properties than the reactants

Energy Flow through Systems

On p. 79, answer Minds On... questions 1-4


1. Which of these processes involve a release of energy?○ Fireworks (a) and the glow stick (d) involve a

release of energy. Fireworks release heat, light, and sound energy. The glow stick releases light energy.

2. Which involve the absorption of energy?○ The boiling water (b) and the baking (c)

involve the absorption of energy. Both absorb heat energy produced by a gas flame or an electric current passing through an element.


3. Which are chemical changes?○ Chemical change involves a change to the

composition of the substance. Therefore, chemical changes occur in (a), (c), and (d).

4. Which are physical changes?○ Physical change involves a change of state

(e.g., liquid to gas). A physical change occurs in (b).

Reactions That Form Gases

Recall: evidence of chemical reactions include the formation of gases and precipitates.

Familiar examples of chemical reactions that result in the formation of gases are breads and cakes rising and the inflation of an automobile air bag.

Reactions That Form Solids

Some reactions form a solid that hardens over a short period of time. Epoxy glue is one example.

Showing States in Chemical Formulas

Recall: (s), (l), (g), (aq) are the subscripts that refer to the substances state at room temperature. It is important to always give as much information as possible about a reaction.

The following are guidelines for the states of substances at room temperature


ElementsMetals are solid, except mercury, which is a

liquidMost of the diatomic elements are gases

H2(g), N2(g), O2(g), F2(g) and Cl2(g). Bromine is a liquid and iodine is a solid: Br2(l) and I2(s)

Sulfur, phosphorus and carbon are solids


CompoundsAll ionic compounds are solid at room temperatureAn ionic compound that is very soluble is shown as

aqueous when it is dissolved in water. An ionic compound that is slightly soluble is usually shown as solid, even when it’s in water.

Molecular compounds are very difficult to predict. The smaller the molecules are, the more they tend to be gases. The larger they are, the more they tend to be liquids and solids. For example, CH4(g) is a gas (natural gas), C6H14(l) is a liquid component of gasoline and C18H38(s) is bees wax.

Energy Changes

Energy flow is an essential part of any chemical reaction, sometimes energy is absorbed and other times energy is released.

Exothermic Reactions THE AUTOMOTIVE BATTERY

A lead-acid storage battery is an electrochemical device that produces voltage and delivers electrical current. The battery is the primary "source" of electrical energy used in vehicles today. It's important to remember that a battery does not store electricity, but rather it stores a series of chemicals, and through a chemical process electricity is produced. Basically, two different types of lead in an acid mixture react to produce an electrical pressure called voltage. This electrochemical reaction changes chemical energy to electrical energy and is the basis for all automotive batteries.

Exothermic reactions – chemical reaction that release energy usually in the form of heat, light or electricity

http://video.google.ca/videosearch?hl=en&q=exothermic+reaction&um=1&ie=UTF-8&ei=O4OASsO9H5OKswP66qDvCg&sa=X&oi=video_result_group&ct=title&resnum=4

Exothermic Reactions

Another important exothermic reaction is the combustion of fossil fuels: coal, oil and natural gas

Combustion – chemical reaction that occurs when oxygen reacts rapidly with a substance to form a new substance and gives off energy (also called “burning”)

http://video.google.ca/videosearch?hl=en&q=exothermic+reaction&um=1&ie=UTF-8&ei=O4OASsO9H5OKswP66qDvCg&sa=X&oi=video_result_group&ct=title&resnum=4#q=combustion+reaction&hl=en&emb=0

Exothermic Reactions

For example, coal is used to produce electricity, the heat released by coal combustion is used to make steam, which drives turbines that produce electricity.

This process produces carbon dioxide, which is a greenhouse gas that contributes to climate change

coal + oxygen carbon dioxide + energy

Endothermic Reactions

Endothermic reaction – chemical reaction that absorbs energy

For example, in a cold pack, it contains chemicals that absorb energy directly from the environment. When you squeeze the package, you break a container inside the pack that keeps the chemicals separate from each other. When they mix and react, they absorb energy and the whole mixture cools down

Biochemical Reactions

Two examples of chemical reactions important to life on Earth are photosynthesis and respiration. These two biochemical reactions (may be endothermic or exothermic) form the basis of life as almost all food produced on Earth begins with photosynthesis.

Characteristics of Chemical Reactions

Recall: All chemical reactions have these characteristicsAll reactions involve the production of new

substances with their own characteristics (state at room temperature, melting point, colour and density)

All reactions involve the flow of energy. This may be detected by a change in temperature during the reaction. Endothermic reactions absorb energy and exothermic reactions release energy.

Characteristics of Chemical Reactions

When new substances form in chemical reactions, sometimes changes of state can be observed. For example, the formation of a gas (bubbles) or a solid (precipitate)

All chemical reactions are consistent with the law of conservation of mass

Any ideas as to what this means?

Conservation of Mass

In 1789, a French chemist, Antoine Lavoisier, came to a very important conclusion. Before we discuss this, try to explain this;

○ Suppose 23.0g of magnesium metal is burned in pure oxygen. When all of the white powder is carefully collected and placed on a scale, its mass is 39.0g. How can it weigh 16g more??

How does this make sense??

http://www.youtube.com/watch?v=dfwHl86wj68&feature=related

Conservation of Mass First, let’s look at Lavoisier’s work. He stated that: when

a system of chemicals reacts completely, the total mass of all of the reactants equals the total mass of the products. In other words, in chemical processes, the most important property to be conserved is the number of atoms of each kind that are present. Unlike nuclear processes, chemical reactions do not create or destroy atoms, or change one kind of atom into another. They only reshuffle the atoms that were originally present into different molecular combinations. What we would like to be able to do is to count each kind of atom before and after a reaction and make sure that none has been gained or lost.

Still...how can you start with 23g and end up with 39g??

Conservation of Mass Is Lavoisier’s conclusion wrong?? No, it’s not wrong, it’s actually telling us that

16g of oxygen reacted with the 23g of magnesium metal. The difference in mass means that there is a reactant that we can’t see – some new form of matter. The difference of mass between the magnesium and white powder product also gives us the mass of this unseen compound.

His conclusion is called the law of conservation of mass

UNIT A: CHEMISTRY

A3.2: Writing Chemical Equations

In this section you will learn about...


○ ROCK – translate word equations to balanced chemical equations and vice versa for chemical reactions that occur in living and non living systems

Writing Chemical Equations

Chemical change involves chemical reactions. To record what occurs in a chemical reaction, chemists use a balanced chemical equation made up of chemical formulas.

Symbolizing Chemical Change To write a chemical equation, you need

to know what substances react (the reactants) and what new substances form (the products). This requires you to;

○ careful observations○ knowledge of what substances are present at

the start of the reaction○ the ability to analyze the materials produced

by the reaction

Symbolizing Chemical Change Recall: chemical change is often

accompanied by visible events such as;○ change in color○ production of gas (bubbles)○ release of heat (increased temperature)○ appearance of a substance that is only slightly

soluble (cloudiness)

Writing Word Equations

Consider the chemical reaction between a piece of magnesium metal with hydrochloric acid. We can describe the reaction with the following sentence;solid magnesium metal reacts with aqueous

hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas.○ Which are the products? Which are the

reactants?


The word equation for this reaction is;

magnesium + hydrochloric acid

magnesium chloride + hydrogen gas

The “+” sign groups the reactants and the arrow separates the reactants from the products (which is read “produces”), then the products are separated by a “+” sign as well


Another example;An iron nail is placed in a solution of copper

(II) chloride

iron + copper (II) chloride iron (II) chloride + copper

Don’t worry about not knowing the products of a chemical reaction, we’ll go through those more in depth later!

Writing Balanced Formula Equations

Formula equation – a chemical equation that uses the reactants and products in a chemical reaction

Because mass is conserved in a chemical reaction, you need to write a balanced formula equation (a formula equation that has the same number of atoms of each element in both the reactants and products)


Let’s look at the formula for water;

hydrogen + oxygen water

H2 (g) + O2 (g) H2O(l)

This is called a skeleton equation because it identifies the substances involved in the reaction but it is not balanced.


How do you know the correct proportions?Recall: the law of conservation of mass – the

mass of the reactants must equal the mass of the products

H2 (g) + O2 (g) H2O(l)

Follow these steps:Count the number of oxygen and balance

H2 (g) + O2 (g) → 2 H2O(l)

Count the number of hydrogen and balance

2 H2 (g) + O2 (g) → 2 H2O(l)

→


Try the following

N2 (g) + H2(g) → NH3(g)

Count the number of nitrogen and balance

N2 (g) + H2(g) → 2NH3(g)

Count the number of hydrogen and balance

N2 (g) + 3H2(g) → 2NH3(g)


There is no specific element to try to balance first, if you’re having trouble with one element and it won’t seem to balance then start with one of the other elements first!


Try to balance the following:a. O2 (g) + CH4(g) → CO2(g) + H2O(g)

2O2 (g) + CH4(g) → CO2(g) + 2H2O(g)

b. Fe(NO3)2(aq) + Na3PO4(aq) → NaNO3(aq) + Fe3(PO4)2(s)

3Fe(NO3)2(aq) + 2Na3PO4(aq) → 6NaNO3(aq) + Fe3(PO4)2(s)

UNIT A: CHEMISTRY

A3.3: Five Common Types of Chemical Reactions



○ ROCK – classify and identify categories of chemical reactions (formation, decomposition, hydrocarbon combustion, single replacement, double replacement)

○ ROCK – predict the products of formation (synthesis) and decomposition, single and double replacement and hydrocarbon combustion chemical reactions, when given the reactants

Five Common Types of Chemical Reactions

Chemists have looked at many different types of reactions and found some common characteristics. From the vast array of reactions, a few types have emerged and have also allowed us to predict the outcome of many chemical reactions by examining the reactants.

The five common types of chemical reactions are formation, decomposition, hydrocarbon combustion, single replacement and double replacement

Formation Reactions

Formation reaction – two elements combine to form a compound (also known as composition or synthesis)element + element = compound

ORA + B = AB

Formation Reactions

Example:Word Equation:

○ sulfur + oxygen sulfur dioxideSkeleton Equation:

○ S8(s) + O2(g) SO2(g)

Balanced Equation:○ 1S8(s) + 8O2(g) 8SO2(g)

Formation Reactions

On your own, try Write the skeleton equation and balanced

equation for the following○ formation of lithium oxide from its elements.○ formation of lead (IV) bromide from its

elements.○ formation magnesium oxide○ Formation of iron (III) chloride

Formation Reactions

Skeleton Equation:Li(s) + O2(g) Li2O(s)

Balanced Equation:4Li(s) + 1O2(g) 2Li2O(s)

Skeleton Equation:Pb(s) + Br2(l) PbBr4(s)

Balanced Equation:Pb(s) + 2Br2(l) PbBr4(s)

Formation Reactions

Skeleton Equation:Mg(s) + O2(g) MgO(s)

Balanced Equation:2Mg(s) + 1O2(g) 2MgO(s)

Skeleton Equation:Fe(s) + Cl2(g) FeCl3(s)

Balanced Equation:2Fe(s) + 3Cl2(g) 2FeCl3(s)

Decomposition Reactions

Decomposition reaction – products that can be broken down into its reactantscompound = element +

element

ORAB = A + B



○ aluminum chloride aluminum + chlorineSkeleton Equation:

○ AlCl3(s) Al(s) + Cl2(g)

Balanced Equation:○ 2AlCl3(s) 2Al(s) + 3Cl2(g)


On your own, try Write the balanced equation for the following

○ solid magnesium sulfide produces solid magnesium and solid sulfur

○ solid potassium iodide produces solid potassium and solid iodine

○ solid aluminum oxide produces solid aluminum and oxygen gas

○ solid nickel (II) chloride produces solid nickel and chlorine gas


Balanced Equation:8 MgS(s) 8 Mg(s) + S8(s)

Balanced Equation:2 KI(s) 2 K(s) + I2(s)

Balanced Equation:2 Al2O3(s) 4 Al(s) + 3 O2(g)

Balanced Equation: NiCI2(s) Ni(s) + Cl2(g)

Hydrocarbon Combustion Reactions

Hydrocarbon Combustion reaction – substances that contain hydrogen and carbonCxHy + O2(g) CO2(g) + H2O(g)

ORhydrocarbon + oxygen produces

carbon dioxide + water



○ methane + oxygen carbon dioxide + waterSkeleton Equation:

○ CH4(g) + O2(g) CO2(g) + H2O(g)

Balanced Equation:○ CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)


On your own, Complete and balance each equation

○ C2H6(g) + O2(g)

○ C3H8(g) + O2(g)

○ C 6 H14(g) + O2(g)

○ C6H6(l) + O2(g)


On your own, Complete and balance each equation

○ 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O (g)

○ C3H8(g) + 5 O2(g) 3 CO2(g) + 4 H2O (g)

○ 2 C6H14(l) + 19 O2(g) 12 CO2(g) + 14 H2O(g)

○ 2 C6H6(l) + 15 O2(g) 12 CO2(g) + 6 H2O (g)

Single Replacement Reactions

Single Replacement reaction – a reactive element reacts with an ionic compound, after the reaction the element ends up in a compound and one of the elements in the reactant ends up as an elementA + BC = AC + B



○ magnesium + silver nitrate silver + magnesium nitrate

Skeleton Equation:○ Mg(s) + AgNO3(aq) Ag(s) + Mg(NO3)2 (aq)

Balanced Equation:○ Mg(s) + 2 AgNO3(aq) 2 Ag(s) + Mg(NO3)2(aq)



○ aluminum is added to copper (II) chloride, which produces copper and aluminum chloride

○ bromine is mixed with iron (III) iodide to produce iodine and iron (III) bromide

○ chlorine gas is added to a solution of aqueous nickel (III) bromide and the mixture is stirred; it produces aqueous nickel (III) chloride and liquid bromine

○ zinc metal is placed into a solution of silver nitrate and allowed to sit. This produces aqueous zinc nitrate and solid silver metal


Balanced Equation:2 Al(s) + 3 CuCl2(aq) 3 Cu(s) + 2 AlCl3(aq)

Balanced Equation:3 Br2(s) + 2 FeI3(aq) 3 I2(s) + 2 FeBr3(aq)

Balanced Equation:3 Cl2(g) + 2 NiBr3(aq) 3 Br2(s) + 2

NiCl3(aq)

Balanced Equation: Zn(s) + 2 AgNO3(aq) 2 Ag(s) + Zn(NO3)2(aq)

Double Replacement Reactions

Double Replacement reaction – the ions in the first compound join with ions in the second compoundAB + CD = AD + BC



○ lead (II) nitrate + sodium iodide lead (II) iodide + sodium nitrate

Skeleton Equation:○ Pb(NO3)2(aq) + NaI(aq) NaNO3(aq) + PbI2(aq)

Balanced Equation:○ Pb(NO3)2(aq) + 2 NaI(aq) 2 NaNO3(aq) + PbI2(aq)



○ when aqueous copper (I) nitrate and aqueous magnesium bromide are mixed, a precipitate of solid copper (I) bromide forms along with aqueous magnesium nitrate

○ when aqueous aluminum chloride and aqueous sodium hydroxide are mixed, a precipitate of solid aluminum hydroxide forms as well as aqueous sodium chloride


Balanced Equation:○ 2 CuNO3(aq) + MgBr2 (aq) Mg(NO3)2(aq) + 2 CuBr(s)

Balanced Equation:○ 3 NaOH(aq) + AlCI3(aq) Al(OH)3(s) + 3 NaCl(aq)

UNIT A: CHEMISTRY

A3.4: The Mole



○ ROCK – interpret balanced chemical equations in terms of moles of chemical species and relate the mole concept to the law of conservation of mass

○ SAND – define the mole as the amount of an element containing 6.02 X 1023 atoms (Avogadro’s number) and apply the concept to calculate quantifies of substances of other chemical species

Did you know??

Mole day is celebrated on October 23 each year. It begins at 6:02 am and ends at 6:02 pm. The numbers are associated with these dates and times derived from Avogadro’s number, a constant known to all chemists in the world. It’s value is approximately 6.02 X 1023

The Mole

Chemists deal with atoms and molecules all the time, and they need to measure quantities of matter precisely. Balanced equations indicated the correct proportion of atoms and molecules to use in a reaction.

Since atoms and molecules are very small, the quantity used to measure them needs to be a very large number.

Molar Mass

Molar mass – the mass of one mole of a substance

Experiments have been done to determine the atomic molar mass (found on the periodic table), you can use the atomic molar mass to find the molar mass of any substance

Avogadro’s Number and the Mole

Mole – the quantity that chemists use to measure elements and compounds (symbol: mol)

The number of particles in 1 mol is called Avogadro’s number (6.02X1023)

To define the mole, chemists chose to work with an isotope of the element carbon-12. Carbon is a stable solid, so it is easy to work with. You will learn more about this in Chemistry 20!!

Molar Mass of Metals

What is the molar mass of the following metals? Give the symbol and then write the molar mass.Calcium – Ca, 40.08 g/molLithium – Li, 6.94 g/molCopper – Cu, 63.55 g/molSilver – Ag, 107.87 g/molTungsten – W, 183.84 g/mol

Molar Mass of Polyatomic Elements

What is the molar mass of the following polyatomic elements? Give the symbol and then write the molar mass.Oxygen – O2, 32.00 g/mol

Fluorine - F2, 38.00 g/mol

Hydrogen – H2, 2.02 g/mol

Sulfur – S8, 256.56 g/mol

Phosphorus – P4, 123.88 g/mol

Molar Mass

What is the molar mass of methane?formula: CH4 (g) – contains one carbon atom

and four hydrogen atomsH = 1.01 g/mol X 4 = 4.04 g/molC = 12.01 g/mol X 1 = 12.01 g/molAdd them together to get 16.05 g/mol

Therefore the molar mass for one molecule of methane is 16.05 g/mol.

Molar Mass

Find the molar mass of the following compoundsMgOLi2S

Ga2Se3

CaCO3

Cr3(PO3)2

C8H18

Molar Mass

Find the molar mass of the following compoundsMgO - 40.31 g/molLi2S – 45.95 g/mol

Ga2Se3 – 376.32 g/mol

CaCO3 – 100.09 g/mol

Cr3(PO3)2 – 313.94 g/mol

C8H18 – 114.26 g/mol

Molar Mass

Find the molar mass of the following compoundsStrontium chloridePotassium phosphideManganese (II) nitrideAluminum chromateGlucoseCobalt (III) sulfite

Molar Mass

Find the molar mass of the following compoundsStrontium chloride – SrCl2 – 158.52 g/mol

Potassium phosphide – K3P – 148.28 g/mol

Manganese (II) nitride – Mn3N2–192.84g/mol

Aluminum chromate – Al2(CrO4)3 – 401.96 g/mol

Glucose – C12H22O11 – 342.34 g/mol

Cobalt (III) sulfite – Co2(SO3)3 – 358.07g/mol

Molar Mass

In other words, to find mass:

m = n X M

where

m is the quantity of matter in grams (g)

n is the quantity of matter in moles (mol)

M is the molar mass (g/mol)

The Factor-Label Method of Converting between Quantities

This is used for converting between the number of moles of a substance and its mass.Because 1 mol C = 12.01g C their ratio has a

value of 112.01g C = 1 The fraction is called a “factor”

1 mol C and the units are called “labels”To find 3.000 moles of carbon: Since this is a

moles-to-mass conversion, we choose the factor that has “mole” in the denominator so it will cancel out the “mol” in 3.000 mol.

mc= 3.00 mol X 12.01g

1 mol

The Factor-Label Method of Converting between Quantities

mc= 3.00 mol X 12.01g = 36.03 g C

1 mol

Try the following

a. How many moles of silicon are in a 56.18 g sample?

○ n = m = 56.18g = 2.000 mol

M 28.090 g/mol

b. What is the mass of 10.0 mol of water?○ m = n X M

m = 10.0 mol X 18.02 g/mol

m = 180 g of water

The Mole Concepts and the Law of Conservation of Mass

Recall: the law of conservation of mass states that, in any reaction, the total mass of the reactants equals the total mass of the products.

When chemists read equations that have been balanced, they often read the coefficients as moles. One reason is that you can see a mole of something, while it is impossible to see an atom of something. Another reason is that chemists use the mole to measure out chemicals.

The Mole Concepts and the Law of Conservation of Mass

For example, consider the reaction of sodium metal with oxygen gas

word: sodium + oxygen sodium oxide

balanced: 4 Na(s) + O2(g) 2Na2O(s)

you can read it as:

4 atoms Na(s) + 1 molecule O2(g) 2 molecules Na2O(s)

it can also be read as:

4 moles Na(s) + 1 mole O2(g) 2 moles Na2O(s)

Did you know??

If you had Avogadro’s number of toonies, or 1 mol of toonies, they would cover all of Canada to a height of about 60 km and all of Earth to a height of about 1 km.

chemical change is a process that involves recombining atoms and energy flows

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