1. Mr. Conkey Physical Science Ch.7
Chemical Reactions
Mr. Conkey Physical Science Ch.7

2. Chemical Equations
Reactants – the substances that undergo change in a chemical reaction.
Products – The new substances formed as a result of a chemical reaction
Reactants Products
Chemical Equation – a representation of a chemical reaction in which reactants and products are represented as formulas

3. Conservation of Mass
The law of conservation of mass states that mass neither created nor destroyed in a chemical reaction.
Example: How is the law of conservation of mass represented with a piece of charcoal?

4. Conservation of Mass (Cont.)

5. Balancing Equations
Water is formed by the reaction of hydrogen and oxygen. The reaction can be described by a chemical equation.
H₂ + O₂ H₂O
A chemical equation must be balanced in order to show that mass is conserved in a chemical reaction.

6. Balancing equations (Cont.)
Coefficients – The numbers that appear before the formulas; these can be changed to balance the equation.
When there is no coefficient in front of the chemical formula, then it is understood to be 1.
***Subscripts should never be changed !!!

7. Steps to Balancing Equations
Step 1: Count the number of atoms of each element on each side of the equation
Step 2: The next step is to change one (or more) of the coefficients until the equation is balanced
Step 3: Check to see if all of the Coefficients can be reduced (if possible).

8. Now try to Balance The formula for H₂O

9. Balancing H₂O

10. Lets balance this!
Cu O₂ CuO

11. Understanding Moles
A Counting unit called a mole is used to measure amounts of a substance due to the large number of small particles in that substance
Mole – an amount of a substance that contains approximately 6.02 X 10 ²³ atoms, molecules, or ions of that substance
Avogadro’s number

12. Molar Mass and Conversions
Molar Mass - the mass of one mole of a substance.
The molar mass of a substance can allow you to convert from moles to mass and mass to moles.
Example: The molar mass of CO₂ is 44.0 grams. Therefore, one mole of CO₂ is equal to 44.0 grams.
Expressed as a conversion factor: 44.0 g CO₂/1 mol CO₂ or 1 mol CO₂/44.0 g CO₂ ; If you have 55.0g of CO₂ then you can calculate how many moles…

13. Chemical Calculations
In a chemical reaction, the mass of a reactant or product can be calculated using a balance chemical equation and molar masses of the reactants and products.
Another conversion example: Calculate how much oxygen is needed to make 144 g of H₂O.
Remember the balanced chemical equation of H₂O?
Conversion set up: 144 g H₂O X 1 mol H₂O/ 18.0 g H₂O = 8.00 mol H₂O

14. Using Molar Masses to show equal masses of products/reactants

15. Mole Ratios of H₂O
Balanced chemical equation for H₂O stated in moles: Two moles of hydrogen react with one mole of oxygen to produce two moles of water.
Written as a mole ratio: 1 mol O₂ 2 mol H₂O mol H₂O mol O₂
Converting moles of H₂O to moles of O₂: 8.0 mol H₂O X 1 mol O₂/2 mol H₂O = mol O₂ ; Moles to mass converstion: 4.00 mol O₂ X g O₂/ 1 mol O₂ = 128 g O₂.

16. Classifying Reaction Types
Some general types of chemical reactions include synthesis, decomposition, single-replacement reactions, double-displacement reactions, and combustion reactions.
Type 1: Synthesis:
A reaction is which two or more substances react to form a single substance
Generic equation: A + B AB
Example: 2 Na + Cl₂ NaCl

17. Decomposition
Decomposition reaction – a reaction where a compound breaks down into two or more simpler substances.
Generic equation: AB A + B
Example: 2 H₂O H₂ + O₂
Another: CaCO₃ CaO + CO₂

18. Single Replacement
Single replacement reaction – a reaction in which one element takes the place of another element in a compound.
Generic equation: A BC B + AC
Example: Cu AgNO₃ Ag Cu(NO₃)₂
Another: 2K + 2H₂O H₂ KOH

19. Double Replacement Pb (NO₃)₂ + 2K I Pb I₂ + 2K NO₃
Double-replacement reaction – when two different compounds exchange positive ions and form two new compounds.
Generic equation – AB + CD AD + CB
Examples:
Pb (NO₃)₂ K I Pb I₂ + 2K NO₃
CaCO₃ HCl CaCl₂ + H₂CO₃

20. Combustion reaction
Combustion reaction – a reaction where a substance reacts quickly with oxygen and many times produces heat and light.
Combustion reactions almost always produce oxygen (O₂) and water (H₂O) as products.
Generic equation: C ₓ H ₓ + O₂ X CO₂ + X H₂O
Example:
CH₄ O₂ CO₂ H₂O

21. Some Common Polyatomic Ions

22. Predicting products of Chemical Reactions
Steps to predicting products of chemical reactions:
Step 1 - try to identify what type of reaction is in the equaiton by using the reactants as indicators
Step 2 – Label your reactants based off of their reaction type (i.e. A, B, etc.)
Step 2 – make your prediction based on the generic examples of reaction types (in your reference section)

23. Now Lets Practice What We have Learned!!!!

24. Alas, chapter 7 has come to a close…