1. Chemical Reactions
Test on Friday April 19

2. Chemical Reaction
Chemical Reaction – a change in which one or more substances are converted into new substances
Reactants – substances that react
Products – substances that are produced
Reactants  Products

3. 10 grams HgO = 0.7 grams O + 9.3 grams Hg
Conservation of Mass
Total mass of reactants is always equal to the total mass of products – Antoine Lavoisier
Matter is not created or destroyed; it is conserved.
Law of Conservation of Mass
10 grams HgO = 0.7 grams O grams Hg

4. Father of Modern Chemistry
Lavoisier is known as the Father of Modern Chemistry for this work along with the work he did on types of reactions
Wrote a book called “Elements of Chemistry” in 1790
He developed the nomenclature we use today to describe chemical compounds and reactions.

5. Chemical Equations
A way to describe a chemical reaction using chemical formulas and other symbols.
 produces or forms
+ plus
(s) solid (l) liquid (g) gas (aq) aqueous

6. Coefficients
Coefficients – the numbers in front of the chemical formulas that represent the number of units of each substance taking part in a reaction.
Must be whole numbers
Act like a multiplier and apply to the entire formula
Subscripts – small numbers that tell how many atoms a particular molecule has

7. Sample Equations 2Hg + Br2 → Hg2Br2 Hg2Br2 + 2Cl2 → 2HgCl2 + Br2
2C4H O2 → 8CO2 + 10H2O

8. Balanced Chemical Equations
An equation is balanced if it has the same number of atoms on each side of the equation.
This is due to the Law of Conservation of Matter: Matter cannot be created or destroyed.

9. Steps to Balancing
Write a chemical equation if you don’t already have one.
Remember Oxygen, Chlorine and Hydrogen are diatomic.
Count the atoms on each side.
Choose coefficients that multiply to balance the equation.
Recheck the numbers.

10. Types of Reactions There are 5 types of reactions: Combustion
Synthesis
Decomposition
Single Displacement
Double Displacement

11. Combustion Reactions
When a substance reacts with oxygen to produce energy in the form of heat and light (fire)
Only includes the elements: C, H, and O
Always produces CO2 and H2O
CxHx + O2  CO2 + H2O

12. Element + Element  Molecule
Synthesis Reactions
Two or more substances (elements) combine to form one substance (molecule)
Easily found because there is only one product
Element + Element  Molecule

13. Decomposition Reaction
One substance (molecule) breaks down into multiple substances (elements)
Easily found because there is only one reactant.
Molecule  Element + Element

14. Single Displacement
An element reacts with a molecule. One of the elements in the molecule recombines with the original element.
The reactants and products are both one element and one molecule.
A + BC  AC + B
“unhappy breakup”

15. Double Displacement
The positive ions switch places to form two new compounds.
The reactants and products are always two molecules.
AD + BC  AC + BD
“happy breakup”

16. Activity Series
The Activity Series is a chart that tells which metals will replace other metals in a reaction.

17. Vocabulary
Precipitate – insoluble compound that comes out of a solution
Oxidation – loss of electrons
Reduction – gain of electrons

18. Chemical Reactions and Energy
All chemical reactions either absorb or release energy
Breaking bonds requires energy
Forming bonds releases energy
Energy can take the form of light, heat, sound, or electricity.

19. Exergonic Reactions that release energy are called Exergonic
When that energy is given off as heat its called Exothermic
You can feel the reaction get warmer.

20. Endergonic Reactions that absorb energy are called Endergonic.
When that energy is in the form of heat its called Endothermic.
You can feel the reaction get colder.

21. Catalysts and Inhibitors
A catalyst is a substance that speeds up a reaction.
An inhibitor is a substance used to slow down a reaction or prevent it completely.
The catalyst and the inhibitor do not participate in the reaction. They remain unchanged after the reaction is over.