1. Science 1206

2. Conservation of mass & Balancing equations

3. Chemical Changes
A Chemical change occurs when matter changes into a new and different form.   
For instance when an electric current is passed though liquid water, the water changes into two gasses which are highly flammable; hydrogen and oxygen.

4. Hindenburg Disaster

5. During a chemical reaction, the atoms are neither created nor destroyed. All that really happens to the atoms is that they are rearranged.
Water
Hydrogen
Oxygen
4 H’s and 2 O’s
4 H’s
2 O’s

6. The old substances whose bonds are broken are called reactants
The new substances that are formed as a result of the reaction are called products. (products are produced)
Reactants
Products

7. Energy Changes in Chemical Reactions
the absorption or the release of heat and/or light, sound, electrical energy.
exothermic reactions release energy (exo = out)
endothermic reactions absorb heat (endo = in)

8. Reactions: Heat = energy
The brilliant white light associated with some fireworks is due to the release of energy when magnesium reacts with oxygen.

9. Equations

10. Equations are a way of representing chemical changes/reactions
Chemical Equations
Equations are a way of representing chemical changes/reactions
Chemical changes can be communicated in sentence form or as chemical equations.
Word equations – use of words to DESCRIBE what happens
Chemical (skeleton) equations – use to symbols to SHOW what happens

11. Chemical changes can be communicated in sentence form or as chemical equations.
In a chemical equation, the reactants are listed on the left side of an arrow symbol, and the products are listed on the right side.
A chemical Equation

12. Chemical equations have four parts:
Chemical formulas
Subscripts for the States of matter
(s) solid
(l) liquid
(g) gas
(aq) aqueous - dissolved in water
Numerical coefficients
indicates how many atoms/molecules are involved
Reaction symbols
the "+" sign on the reactants (left) side is read as "reacts with"
the arrow (   ) is read as "to produce"
the "+" sign on the products (right) side is read as "along with".

13. Parts of a Chemical Equation/Reaction
Numerical Coefficients
Subscripts

14. Equation Practice Given the equation: Pick out
A subscript ______________
The symbol meaning “to produce” ______
A chemical formula ____________
The symbol meaning “combines with” _______
A coefficient ______________
A reactant _______________
The symbol meaning “along with” _______

15. Complete the following:
Chemistry Worksheet 2-1

16. Chemical Equations can be translated into a sentence
Words to use for formulas when writing chemical equations as sentences
Formula
Word
Ionic
Formula Unit
Molecular
Molecule
Metal Element
Atom
Nonmetal Element
Let’s Try an Example
Two molecules of diesel fuel reacts with 49 molecules of oxygen to produce 32 molecules of carbon dioxide along with 34 molecules of water.

17. Writing equations as sentences - Practice

18. The Law of Conservation of Mass
In a chemical reaction the mass of the reactants before a chemical reaction equals the mass of the products after the reaction is complete.
mass of reactants = mass products
In other words, the mass you end up with equals the mass you started with.
Ex: Burning Paper is a reaction that obeys the Law of Conservation of Mass
+ Oxygen  +
20 grams

19. the left hand Side = the right hand side
Balancing Equations
Any representation of a chemical equation must reflect the Law of Conservation of Mass
In order to write a chemical equation that obeys the law of conservation of mass, the number of atoms of each element must be the same on both sides of the equation.
the left hand Side = the right hand side
Ex:

20. Balancing Equations - Practice
Let’s have a look at this equation and try to balance it.
Note: To balance equations we write Coefficients in front of each formula.
___ HgO (s)  ___ Hg (l) + ___ O2 (g)

21. Rules for Balancing Equations
When you insert a coefficient, each subscript in the formula is Multiplied by the coefficient.
Ex:
The number of atoms of each element MUST be the same on the left and right sides.
Practice, Practice, Practice

22. Let’s Try another
___ Fe (s) + ___ O2 (g)  ___ Fe2O3 (s)

23. Write a balanced chemical equation for the reaction of cobalt with oxygen to produce cobalt (III) oxide

24. 1.  ___Mg(s)  + ___O2(g)  →  ___MgO(s) 
2.  ___Cu(s)  + ___AgNO3(aq)  →  ___Ag(s) +  ___Cu(NO3)2 (aq)   
3.  ___KI(aq)  + ___Pb(OH)2 (aq)  →  ___PbI2(s) +  ___KOH (aq)
4.  ___P4 (s)  + ___F2 (g)  →  ___PF3 (l)
5.  ___Cr2O3 (s)  →  ___Cr(s) +  ___O2 (g)

25. Practice
Complete the following activities
Chemistry Worksheet 2-2