1. Chapter 23 – Chemical Reactions
23.1 – Chemical Changes

2. Objectives Identify the reactants and products in a chemical reaction.
Determine how a chemical reaction satisfies the law of the conservation of matter.
Determine how chemists express chemical changes using equations

3. Chemical Reactions change one or more substances into new substances
Reactants are substances combine or change
New substances that are produced are called Products

4. Different Reactions
Chemical reactions – use the ELECTRONS to form new substances
Nuclear reactions - use the NUCLEUS to form new substances
What does a chemical reaction look like?

5. Think about it…
If you burned a piece of paper, you end up with a pile of ashes.
Once burned, is there…
More mass?
Same mass?
Less mass?
Why?

6. Conservation of Mass
Law that states, in a chemical reaction, matter is not created or destroyed, but stays the same.
Antoine Lavoisier experimented with mercury (II) oxide and heat
He found mass of products (liquid mercury and oxygen gas) equaled mass of reactants

7. Chemical Equation
Uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces
Chemical formula expresses the relationship between elements in the compound and molecules they make up

8. Chemical Equation Reactants (left) → Products (right)
Arrow means “yields”
SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

9. Coefficients
Numbers which represent the number of units of each substance in a reaction
Knowing coefficients of chemical reactions allows chemists to use the correct amount of reactants to predict the amount of products (law of conservation applies)

10. Example

11. Writing equations (s) solids (aq) aqueous (g) gas (l) liquid
Subscripts are numbers which represent the number of atoms in a molecule of a particular element
Symbols used to show state of reactants
(s) solids
(aq) aqueous
(g) gas
(l) liquid

13. Volcano with a Twist
Reactants?
Products?

14. Equation:
NaHCO3 ( ) + CH3COOH ( ) 
CH3COO-Na+ ( ) + H2O ( ) + CO2 ( )
States?
Conservation?

15. Exit slip on BR paper SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)
What are the reactants?
What are the products?
How is matter conserved?

16. In-class Assignment/Homework
23.1 WKT