Unit 2: Chemistry

Science 10

Name: Block:

Book 3: Chemical Equations & balancing

1

Chemical vs Physical Change

________________is the amount of matter contained in a thing. Usually the mass of common things is measured in ________________ or ______________________.

______________________are the qualities of a thing, especially those qualities common to a group of things. The relationship between matter and its properties is a very important aspect of chemistry.

A p________________________property of a substance is a property that can be found without creating a new substance.

For example:

A c________________________property is the ability of a substance to undergo chemical change/_____________ and change into a __________ substance.

For example:

Physical Properties versus Chemical Properties

The properties of matter are also classified as being either physical properties or chemical properties. Recall, Physical properties describe _________________________________, which are changes of _________________or form. Physical properties also describe the physical________________________of a material.

Chemical properties describe chemical _________________. Chemical changes are those in which a new substance(s) or species is formed (Figure 2.1.2). Chemical properties also describe the tendency of a chemical to _________________________. Chemical properties describe relationships or interactions between different forms of matter.

They include a chemical’s -_________________________________-_________________________________-_________________________________-_________________________________

Most physical properties describe relationships or interactions between matter and energy.

-Hardness__________________________________________________________________________________________-Malleability________________________________________________________________________________________-Ductility__________________________________________________________________________________________-Lustre____________________________________________________________________________________________-Viscosity__________________________________________________________________________________________-Diffusion__________________________________________________________________________________________

For example, A material can be classified as_____________________, _________________________________ or translucent by how it interacts with light. Other physical properties you may have learned about include _________________________________ density, _________________________________, and surface tension. I

Physical properties describe physical changes.

Chemical properties describe interactions between different forms of matter...or chemical change.

Figure 2.1.2 The wood that is burning to heat the pot is undergoing chemical changes. The boiling soup in the pot is undergoing a physical change.

______________________ is the science concerned with the properties, composition, and behaviour of matter. _________________is anything that has mass and occupies space.

2

PHYSICAL AND CHEMICAL PROPERTIES AND CHANGES

Identify the following as a chemical (C) or physical property (P):

______1. blue color

______2. density

______3. flammability (burns)

______4. solubility (dissolves)

______5. reacts with acid

______6. supports combustion

______7. sour taste

______8. melting point ______9. reacts with water ______10. hardness ______11. boiling point ______12. shine ______13. odor ______14. reacts with air

Identify the following as chemical (C) or physical (P) changes.

______1. NaCl (Table Salt) dissolves in water.

______2. Ag (Silver) tarnishes.

______3. An apple is cut.

______4. Heat changes H2O to steam.

______5. Baking soda reacts to vineger.

______6. Fe (Iron) rusts.

______7. Alcohol evaporates .

______8. Ice melts.

______9. Milk sours. ______10. Sugar dissolves in water. ______11. Wood rots. ______12. Pancakes cook. ______13. Grass grows. ______14. A tire is inflated. ______15. Food is digested. ______16. Paper towel absorbs water.______17. An ice cube is placed in the sun.______18. Two chemicals are mixed together and a gas is produced. ______19. A bicycle changes colour as it rusts.______20. A solid is crushed into a powder.______21. Two substances are mixed and light is produced.______22. A piece of ice melts and reacts with sodium.______23. Mixing salt and pepper.______24. Chocolate syrup is dissolved in milk.______25. A marshmallow is toasted over a campfire.______26. A marshmallow is cut in half

Part A: Physical or Chemical?

Assignment #1: Physical & Chemical Properties Part A & B Complete this assignment in the space provided on the following pages

3

Part B

Read each scenario. Decide whether a physical or chemical change has occurred and give evidence for your decision. The first one has been done for you to use as an example.

Scenario Physical or Chemical Change?

Evidence…

1. Umm! A student removes a loaf of bread hot from the oven. The student cuts a slice off the loaf and spreads butter on it.

Physical No change in substances. No unexpected color change, temperature change or gas given off.

2.

Your friend decides to toast a piece of bread, but leaves it in the toaster too long. The bread is black and the kitchen if full of smoke.

3. You forgot to dry the bread knife when you washed it and reddish brown spots appeared on it.

4. You blow dry your wet hair.

5.

In baking biscuits and other quick breads,

the baking powder reacts to release carbon

dioxide bubbles. The carbon dioxide

bubbles cause the dough to rise.

6.

You take out your best silver spoons and

notice that they are very dull and have

some black spots.

7. A straight piece of wire is coiled to form a

spring.

8. Food color is dropped into water to give it

color.

9.

Chewing food to break it down into smaller

particles represents a _________ change,

but the changing of starch into sugars by

enzymes in the digestive system represents

a ___________change.

10. In a fireworks show, the fireworks explode

giving off heat and light.

Part C: True (T) or False (F)?

1. Changing the size and shapes of pieces of wood would be a chemical change.

2. In a physical change, the makeup of matter is changed.

3. Evaporation occurs when liquid water changes into a gas.

4. Evaporation is a physical change.

5. Burning wood is a physical change.

6. Combining hydrogen and oxygen to make water is a physical change.

7. Breaking up concrete is a physical change.

8. Sand being washed out to sea from the beach is a chemical change.

9. When ice cream melts, a chemical change occurs.

10. Acid rain damaging a marble statue is a physical change.

4

What is a chemical reaction?

A _________ is a change that takes place when one or more substances (called _____ -; form one or more __ substances (called ______ ).

reactants products

For example:

+ ➔

+ ➔

+ ➔

How can you spot a chemical reaction?

Chemical reactions can appear very different.

As you observe a chemical reaction, you may detect:

• a _________ change

• __________ (solid) forming

• _____ being produced (heat, light)

• _____ produced (fizzing, bubbles)

• an _____ being produced.

5

A word equation uses the names of the ___________________ and _______________________to show what happens in a chemical reaction.

For example, when a piece of sulfur is burned in oxygen gas it produces a white solid called sulfur dioxide.

The word equation for this reaction is:

A symbol equation uses the_________________________of the reactants and products to show what happens in a chemical reaction. (also called a skeleton equation-because it's NOT balanced...yet!))

A symbol equation MUST be _____________________to give the correct ratio of reactants and products.

This equation shows that ________ atom of sulfur (S) reacts with_______ molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2).

State symbols are added to a symbol equation to show whether the reactants and products are:

• ___________– symbol is (s)

• __________ – symbol is (l)

• __________ – symbol is (g)

• dissolved in __________ – symbol is (aq).

With state symbols in place, this symbol equation now shows that the sulfur is a __________, the oxygen is a __________and the sulfur dioxide is also a __________.

6

Chemical word equations are descriptive but chemical reaction equations are much more efficient.

Using chemical symbols and numbers creates a "chemical shorthand" for all chemists to understand... much like txt language saves our thumbs and shortens convs.

The general form of a chemical equation is:

“Sodium metal reacts with chlorine gas to produce sodium chloride crystals.”

Chemical Word Equation:

Skeleton chemical reaction equation:

Balanced chemical reaction equation:

Quick Check1. Convert the following from a word equation to a formula equation:

Calcium oxide powder is combined with water to form calcium hydroxide solid.______________________________________________________________________________________________________________________________________________________________________________

2. Convert the following from a formula equation to a word equation:H2CO3(aq) ➝ CO2(g) + H2O(l)_______________________________________________________________________________________

Chemical Reaction Equations

7

Assignment # 2: Writing Word Equations pg 8-9Complete this assignment in the space provided on the following pages

8

9

BCS10_C04_F_3 6/9/08 11:51 AM Page 189

B

What happens to atoms of hydrogen and atoms of oxygen when the two gases are brought together and ignited ?

Are new atoms created in the flash?

Are some destroyed?

Figure 4.32 The reaction of oxygen molecules withhydrogen molecules involves rearranging atoms innew ways.

Figure 4.30 The hydrogen and oxygen in the balloon do not react until the balloon is touched by a flame (A). Then, an explosive chemical reaction occurs (B).

�

�

O2(g)2H2(g) 2H2O(g)➔

➔

Law of Conservation of Mass

When a chemical reaction occurs, new compounds are created, BUT…

No new matter is created or destroyed; atoms are just ___________________________ as the atoms change partners to form new compounds.

If there are ___atoms of oxygen in the reactants, THERE MUST BE ____ atoms of oxygen in the products.

Number of each a_______in reactants = number of each a_______in products. This is called THE LAW OF CONSERVATION OF ATOMS. And also explains why we must balance chemical equations.

THE LAW OF CONSERVATION OF MASS

The law of conservation of mass states that mass is conserved in a chemical reaction.

The ____________________of the products is always equal to the ___________________of the reactants in a chemical reaction.

The idea that atoms are ____________________(neither made nor destroyed) is believed to be true for all chemical reactions .

10

Hg O HgO O

mercury(II) oxide, HgO(s) --> Hg(l) + O2(g), shows that it does not obey the law of conservation of mass. The reactant, HgO contains ____________ oxygen atom than the products, Hg and O2.

To show that the mass before and after a chemical reaction occurs remains constant, the formula equation has to be ___________________.

Balancing a chemical equation requires the placement of coefficients in front of reactant and/or product species.

_____________________________are numbers that multiply the entire chemical species that follows them.

These numbers ensure that the number of ________________________ __________________________on the reactant side is equal to those on the product side of the equation.

Figure 4.1.2 The reactant in this reaction weighs less than the products.

It is critical to remember balancing must always involve the placement of coefficients and NEVER the changing of subscripts.

Altering the subscripts will give an incorrect formula for a substance.

Balancing Chemical Equations

Example Balance (NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O The Method

Note: Until you are finished balancing, missing coefficients are treated as zeros!**

Do not start with atoms that are easy or difficult to balance; it’s best to balance them last.Elemental species are easy; elements that occur in more than one species on each side (usually O and H) are tough!

Balance preserved groups (those that don’t come apart) whenever possible.

Find an element that only occurs in one species on each side; these are usually metal ions. Put a coefficient in front of the two species so as to balance the element of interest.

(** Very Important: The 1st step is the only step where you place coefficients on both sides.**)

You have successfully balanced one element. Booyah! The problem has now becomes easier to solve. The coefficients will also have fixed another element (or group) on one side.

Now place a coefficient to balance the atom (or group) on the opposite side.

Repeat the process until all of the elements are balanced.

Omit coefficients of 1 in your final answer. **Always do a check to make sure that all atoms are balanced.**

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

(NH4)3PO4 + NaOH Na3PO4 + NH3 + H2O

A brief examination of the equation for the decomposition of

11

Example 1 Balance K + H2O KOH + H2

Example 2 Balance MoCl3 + O2 + AgCl MoCl4 + Ag2O

12

Assignment #3: Balancing Equations Review pg 13-16Complete this assignment in the space provided on the following pages

13

14

Writing and balancing equations

Skills: Interpreting, Numeracy, Knowledge

1 Define the Law of Conservation of Mass.

2 Apply the Law of Conservation of Mass by balancing the following equations.

a CH4(g> + 0

2<g) - C02<g> + H

20cn

b Klcaq) + - + KN03(aqJ

C Hl04(aq) + KOH(aql

+

d Ales> + A1Cl3<•>

e NH3<g>

+ +

You must apply the following steps to write balanced chemical equations. • Write the word equation for the reaction.• Directly underneath the word equation, write the unbalanced formula equation.• Add subscripts-(s), (1), (g) or (aq).• Balance the equation.

Note: Dilute means a solution with water and therefore the appropriate subscript is (aq).

The table below lists various compounds and the chemical formula of each compound.

Compound name Compound formula Compound name Compound formula

Hydrochloric acid HCI

Nitric acid HN03

Sulfuric acid H2S0

4

Magnesium chloride MgCl2

Barium sulfate BaS04

Sodium sulfate N3iS04

Water H20

Carbon dioxide

Calcium carbonate

Calcium nitrate

Magnesium hydroxide

Barium nitrate

Sodium hydroxide

Sodium carbonate

CO2

CaC03

Ca(N03)2

Mg(OH)2

Ba(N03

)2

NaOH

N3iC03

Science Focus 4 Homework Book 3 15

Chemical e uations page 2

Writing and balancing equations

Skills: Interpreting, Numeracy, Knowledge

3 Use the information in the table on page 1 of this worksheet to construct balanced chemical equations, including subscripts, for each of the following reactions.

a Dilute hydrochloric acid is added to solid magnesium hydroxide, producing water and the soluble salt magnesium chloride.

b Dilute nitric acid is added to solid calcium carbonate, producing bubbles of carbon dioxide, water, and the soluble salt calcium nitrate.

c When dilute sodium sulfate solution is added to dilute barium nitrate solution, barium sulfate precipitates, leaving sodium nitrate in solution.

d Dilute sodium hydroxide is added to dilute sulfuric acid, producing water and the soluble salt sodium sulfate.

e Dilute sulfuric acid is poured over solid sodium carbonate, producing carbon dioxide, water and the soluble salt sodium sulfate.

4 Construct balanced equations, including subscripts, for the following reactions. You may need to use the cross method from Worksheet 1.1 to construct the chemical formulas first on a separate sheet of paper.

a Iron metal reacts with chlorine gas to produce iron chloride.

b Sodium chloride solution is mixed with silver nitrate solution, producing a precipitate of solid silver chloride.

c Lead nitrate solution is added to sodium sulfate solution, producing lead sulfate precipitate.

d Sulfur dioxide gas reacts with oxygen to produce sulfur trioxide gas.

16