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Mr. Conkey Physical Science Ch.7

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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…


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