Unit 7 Chemical Reactions

**Reactants → Products Left side (reactants) = Right side (products) 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)

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.

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.

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

+ 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.

2H2 + O2 → 2H2O What are the reactants? What are the products? What are the coefficients for the whole reaction?

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.

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.

Diatomic Elements Element w/ 2 atoms H2, N2, O2, F2, Cl2, Br2 & I2

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

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

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.

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

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

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:

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.

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

Combine the 2 elements into a compound Practice: 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 →

1. Aluminum + Magnesium oxide → 2. Copper (II) sulfide + chlorine → 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 →

Switch the position of the (+) ions. Practice: 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 →

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.

Metallic Hydroxides: MOH  MO + H2O Substitute the specific + ion for the “ M “ and follow the word equation.

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

Simple Decomposition: AB  A + B Split the compound into is simpler parts.

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 →