Unit 7 Chemical Reactions

1
Unit 7Chemical Reactions

• Ch. 8 19.1

2
Equations

• An equation is a description of a chemical
  reaction indicating the reactants, the products
  and a ratio of their quantities.
• REMEMBER
• Reactants ? Products
• Left side (reactants) Right side (products)

3

• Coefficients -- numbers placed in front of
  chemical formulas in a reaction.
• The reaction is said to go to completion when no
  reactants remain when the reaction has stopped.
• The reaction may be reversible. When this
  happens, a complete cycling of events exists. It
  is a continuous ongoing process.

4

• Law of Conservation of Mass
• In reactions atoms are neither created nor
  destroyed only rearranged.
• The Law of Conservation of Mass governs most
  chemical reactions.

5

• What is the relationship between the mass of the
  reactants and the mass of the products?
• How are chemical reactions balanced?

6

• signs are used to separate reactants or
  products on the same side of the arrow.
• Catalyst is a substance that speeds up the rate
  of a reaction. This is neither a reactant nor
  product. Write its formula above arrow.

7
2H2 O2 ? 2H2O

• What are the reactants?
• What are the products?
• What are the coefficients for the whole reaction?

8
Rules for Balancing Equations

• Determine the correct formula for all reactants
  and products. Indicate physical states in
  parentheses.
• Write the formulas for the reactants on the left
  and the products on the right of the arrow.
  Separate two or more formulas with signs.
• Count the number of atoms of each element for
  both sides of the equation.

9

• Balance the elements one at a time by using
  coefficients.
• Check each atom to be sure that the equation is
  balanced.
• Make sure the coefficient Are in the lowest
  whole number ratio that balances.

10
Diatomic Elements

• Element w/ 2 atoms
• H2, N2, O2, F2, Cl2, Br2 I2

11
Classifying reactions

• Synthesis (Combination) reaction 2 or more
  substances combine to form one product.
• The reactants can be elements or compounds.
• The product will always be a compound.
• A B ? AB
• Decomposition reactions a single compound is
  broken down into simpler components.
• The reactant is always a compound
• Most decomposition Reactions requires energy such
  as light, heat or electricity.
• AB ? A B

12

• Single replacement reactions one element
  replaces a second element found in a compound.
• Single elements changes places with the other
  ion that is the same as the single element. ()
  changes with () (-) changes with (-)
• A BC ? AC B

13

• Double Replacement involves the exchange of
  positive ions (cations) between two reacting
  compounds.
• AB CD ? CB AD
• Combustion Reactions an element or compound
  reacts with oxygen often producing energy as heat
  and light.

14
Factors Effecting Reaction Rates

• Temperature raising the temp. speeds up
  reactions. Lowering temp. slows down reactions.
• Concentration increasing the concentration of
  the reactants speeds up the reaction
• Catalyst a substance that increases the rate of
  a reaction without being used up in the reaction.
  Allow reaction to occur at a lower temperature.
• Inhibitor a substance added that interferes
  with the action of a catalyst. Can slow or even
  stop a reaction

15

• Neutralization a reaction in which an acid and
  base react in an aqueous solution to salt and
  water.

16
Predicting Products

• To predict products of any reaction the first
  step is to identify the type of reaction it is.
• Then apply existing rules for the type of
  reaction it is

17
Activity Series of Metals

• Activity Series of metals an invaluable aid to
  predicting the products of replacement reactions.
  It also can be used as an aid in predicting
  products of some other reactions.

18

• Going from bottom to top, the metals
• increase in reactivity
• lose electrons more readily to form positive
  ions
• corrode or tarnish more readily
• require more energy (and different methods) to be
  separated from their ores
• become stronger reducing agents

19

• Synthesis (Combination) element element ?
• Combine the 2 elements into a compound
• Practice
• 1. Aluminum Oxygen ?
• 2. Chlorine Potassium ?
• 3. Chromium Bromine ?
• 4. Oxygen Hydrogen ?
• 5. Calcium Iodine ?

20

• Single replacement element compound ?
• If the element forms a ion replace the ion of
  the compound, and if it is a - ion the replace
  the ion of the compound.
• Practice
• 1. Aluminum Magnesium oxide ?
• 2. Copper (II) sulfide chlorine ?
• 3. Fluorine Nickel bromide ?

21

• Double Replacement compound compound ?
• Switch the position of the () ions.
• Practice
• 1. Aluminum sulfite Calcium acetate?
• 2. Tin (IV) phosphate Ammonium dichromate ?
• 3. Magnesium chloride Chromium peroxide ?

22
Decomposition Reactions

• Metallic Chlorates
• MClO3 ? MCl O2
• Substitute the specific ion for the M and
  follow the word equation.
• Metallic Carbonates
• MCO3 ? MO CO2
• Substitute the specific ion for the M and
  follow the word equation.

23

• Metallic Hydroxides
• MOH ? MO H2O
• Substitute the specific ion for the M and
  follow the word equation.

24

• Oxy Acids
• Write the Oxy acid formula. Water will be a
  product and you must balance water first. Then
  write what elements and their amounts that are
  left over to balance the equation.
• Example
• H2SO4 ? H2O SO3

25

• Simple Decomposition
• AB ? A B
• Split the compound into is simpler parts.

26
Practice

• 1. Potassium sulfide ?
• 2. Zinc oxide ?
• 3. Zinc carbonate ?
• 4. Sodium carbonate ?
• 5. Calcium hydroxide ?
• 6. Aluminum hydroxide ?
• 7. Potassium chlorate ?
• 8. Calcium chlorate ?