Science 10Science 10

Investigating Chemical Reactions!Investigating Chemical Reactions!

Chemical ReactionsChemical Reactions

Magnesium (Mg) and Oxygen (OMagnesium (Mg) and Oxygen (O22))Before Burning: Before Burning:

Mg: silver colour, lightweight, metal.Mg: silver colour, lightweight, metal.OO22: invisible gas in air.: invisible gas in air.

After burning: white powder.After burning: white powder.

Chemical ReactionsChemical Reactions

A A chemical reactionchemical reaction is is the process that leads to the process that leads to a chemical change in a chemical change in which which new substancesnew substances with with new propertiesnew properties are are formed.formed.

They can be summarized They can be summarized 2 ways…2 ways…

Chemical ReactionsChemical Reactions

1. As a word equation1. As a word equation i.e.: magnesium plus oxygen react to produce i.e.: magnesium plus oxygen react to produce

magnesium oxide.magnesium oxide.Or a generic equation: Or a generic equation:

reactant(s) yield(s) product(s)reactant(s) yield(s) product(s)2. As an equation using formulas:2. As an equation using formulas:

i.e.: i.e.: Mg + OMg + O22 → MgO → MgO

Antoine LavoisierAntoine Lavoisier Who?: Who?:

French Nobleman (aristocracy)French Nobleman (aristocracy) Wealthy familyWealthy family Tax collector before the French Tax collector before the French

RevolutionRevolution Beheaded during the Revolution Beheaded during the Revolution

(1794) during the Reign of (1794) during the Reign of Terror.Terror.

When?:When?: Late 1700’s, during the French Late 1700’s, during the French

Revolution Revolution Where?: Where?:

FranceFrance

Antoine LavoisierAntoine Lavoisier

Discoveries he made:Discoveries he made:1. Named oxygen and 1. Named oxygen and

hydrogen as elements.hydrogen as elements.2. Helped develop the 2. Helped develop the

metric system.metric system.3. Developed the “3. Developed the “Law of Law of

Conservation of MassConservation of Mass”.”.

The Law of Conservation of MassThe Law of Conservation of Mass

In any chemical reaction the total mass In any chemical reaction the total mass of the reactants will always equal the of the reactants will always equal the total mass of the products.total mass of the products. (As long as (As long as the reaction is the reaction is closedclosed))What goes in, must come out!What goes in, must come out!

Mass is neither lost nor gained in a chemical reaction!!!

The Law of Conservation of AtomsThe Law of Conservation of Atoms

In any chemical reaction, atoms are In any chemical reaction, atoms are neither created nor destroyed.neither created nor destroyed.

So…Mg + So…Mg + OO22 → Mg → MgOO is not a balanced is not a balanced

reaction.reaction.

AssignmentAssignment

C.Y.U. 9.1 p. 234.C.Y.U. 9.1 p. 234.# 1,2,5,6,8,9 in point form.# 1,2,5,6,8,9 in point form.# 4 & 7 in complete sentences.# 4 & 7 in complete sentences.

Balancing Chemical EquationsBalancing Chemical Equations

Let’s combine Let’s combine sodiumsodium and and chlorinechlorine in a in a chemical equation:chemical equation:Na + ClNa + Cl22 → NaCl → NaCl Reactants yield productsReactants yield productsThis is a skeleton equation; correct formula, This is a skeleton equation; correct formula,

but it is not balanced.but it is not balanced.

Note: chlorine is a Note: chlorine is a diatomic diatomic element. What are the other element. What are the other diatomic elements?diatomic elements?

-Cl-Cl22, H, H22, N, N22, O, O22, F, F22, Br, Br22, I, I22

Balancing Chemical EquationsBalancing Chemical Equations

All chemical equations must obey 2 laws All chemical equations must obey 2 laws of basic chemistry:of basic chemistry:The law of conservation ofThe law of conservation of atomsatoms

In any chemical reactions, atoms are neither In any chemical reactions, atoms are neither created nor destroyed.created nor destroyed.

The law of conservation of massThe law of conservation of massIn any chemical reaction, the mass of the reactants In any chemical reaction, the mass of the reactants

always equals the mass of the products,always equals the mass of the products,

Balancing Chemical EquationsBalancing Chemical Equations

Let’s balance the equation:Let’s balance the equation:Na + ClNa + Cl22 → NaCl → NaCl

The balanced equation must have the same The balanced equation must have the same number of Na and Cl on each side:number of Na and Cl on each side:22Na + ClNa + Cl22 → → 22NaClNaCl

Let’s see how this is done…

Balancing Chemical EquationsBalancing Chemical Equations

1. Cu2S + O2 → Cu2O + SO2 How many Cu atoms are in the reactants? ___ in the products?___ What coefficient(s) will make the number of Cu

atoms in the reactants and products equal?___ How many S atoms are in the reactants?___ in the products?___ What coefficient(s) will make the number of S

atoms in the reactants and products equal?___

Balancing Chemical EquationsBalancing Chemical Equations

Cu2S + O2 → Cu2O + SO2 How many O atoms are in the reactants? in the

products?___ What coefficient(s) will make the number of O atoms in

the reactants and products equal?___ Do any coefficients need to be changed? ___

Rewrite the equation and balance:

2Cu2S + 3O2 → 2Cu2O + 2SO2

Balancing Chemical EquationsBalancing Chemical Equations

So when balancing a chemical equation So when balancing a chemical equation ask yourself:ask yourself:How many atoms of each element are in the How many atoms of each element are in the

reactants?reactants?How many atoms of each element are in the How many atoms of each element are in the

products?products?What coefficients do I need to make the What coefficients do I need to make the

equal? equal? You might need to use lowest common multiples to You might need to use lowest common multiples to

figure it out.figure it out.You might need to add coefficients to elements You might need to add coefficients to elements

that started out equal.that started out equal.

Balancing Chemical EquationsBalancing Chemical Equations

Balancing Chemical EquationsBalancing Chemical Equations

Balancing Chemical EquationsBalancing Chemical Equations