1. Chemical Reactions
Unit 5

2. Word Equations
To write a word equation, write the names of the _________________ to the left of the arrow separated by plus signs; write the names of the ______________ to the right of the arrow, also separated by plus signs.
Examples: Reactant + Reactant  Product + Product
methane + oxygen  carbon dioxide + Water
iron + oxygen  iron(III) oxide
hydrogen peroxide  water and oxygen
a) When methane gas burns, it combines with oxygen to form carbon dioxide and water. b) Iron turns to red-brown rust (iron(III) oxide) in the presence of oxygen in the air. c) Hydrogen peroxide decomposes to water and oxygen when used as an antiseptic.

3. Rules for Writing and Balancing Equations
1. Determine the correct formulas for all the reactants and products. 2. Write the skeleton equation by placing the formulas for the reactants on the left and the formulas for the products on the right with a yields sign (→) in between. If two or more reactants or products are involved, separate their formulas with plus signs. 3. Determine the number of atoms of each element in the reactants and products. Count a polyatomic ion as a single unit if it appears unchanged on both sides of the equation.
4. Balance the elements one at a time by using coefficients. When no coefficient is written, it is assumed to be 1. Begin by balancing elements that appear only once on each side of the equation. Never balance an equation by changing the subscripts in a chemical formula. Each substance has only one correct formula. 5. Check each atom or polyatomic ion to be sure they are equal on both sides of the equation. 6. Make sure all the coefficients are in the lowest possible ratio.

4. Chemical Equations
A chemical equation is a representation of a chemical ________________; the formulas of the reactants (on the left) are connected by an arrow (yield) with the formulas of the products (on the right).
A ________________ equation is a chemical equation that does not indicate the relative _______________ of the reactants and products.
Here is the equation for the reaction that produces rust:
Fe + O2  Fe2O3

5. Writing Chemical Equations
A ______________ is a substance that speeds up the reaction but is ________ used up in the reaction.
Without Catalyst With Catalyst
Hydrogen peroxide decomposes to form water and oxygen gas. a) Bubbles of oxygen appear slowly as decomposition proceeds. b) With the addition of the catalyst manganese(IV) oxide (MnO2), decomposition speeds up. The white “smoke” is condensed water vapor.

7. Example of Chemical Equations
This is a balanced equation for making a bicycle. The numbers are called coefficients—small whole numbers that are placed in front of the formulas in an equation in order to balance it.

8. Describing Chemical Reactions
A chemical reaction is also described by a _______________ equation in which each side of the equation has the same number of atoms of each element and mass is _________________.

9. Reaction Types
The __________ general types of reaction are combination, decomposition, _________- replacement, ___________-replacement and combustion.
The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products.

10. Combination Reactions
A combination or _______________ reaction is a chemical change in which two or more substances react to form a _______________ new substance.
When ignited, magnesium ribbon reacts with oxygen in the surrounding air to form magnesium oxide, a white solid. This is a combination reaction. Observing Why do you think this reaction was once used in flashbulbs for photography?

11. Decomposition Reactions
A decomposition reaction is a chemical change in which a _____________ compound breaks down into _______ or more simpler products.
When orange-colored mercury(II) oxide is heated, it decomposes into its constituent elements: liquid mercury and gaseous oxygen. Comparing and Contrasting How are the two reactions pictured so far similar? How are they different?

12. Single-Replacement Reactions
A single-replacement reaction is a chemical change in which _______ element replaces a second element in a __________________.
The alkali metal potassium displaces hydrogen from water and forms a solution of potassium hydroxide in a single-replacement reaction. The heat of the reaction is often sufficient to ignite the hydrogen. Inferring Why are alkali metals stored under mineral oil or kerosene?

13. Double-Replacement Reactions
A double-replacement reaction is a chemical change involving an exchange of _________________ ions between two compounds.
Double-replacement reactions always involve two ionic compounds.
Aqueous solutions of potassium carbonate and barium chloride react in a double-replacement reaction to form the white precipitate barium carbonate. Potassium chloride, the other product of the reaction, remains in solution.

14. Combustion Reactions
A combustion reaction is a chemical change in which an element or a compound reacts with __________________, often producing energy in the form of heat and light.
Methane gas reacts with oxygen from the surrounding air in a combustion reaction to produce carbon dioxide and water. Inferring What else is produced in this reaction?

15. Activity Series
The activity series of metals lists metals and ___________ in order of decreasing reactivity.

16. General Reaction Equations

17. General Reaction Equations

18. General Reaction Equations
Remember that there are two possible types of combustion reactions.
Complete combustion reactions yield carbon dioxide and water.
Incomplete combustion reactions yield carbon monoxide and water.

19. Ionic Equations
A _______ ionic equation shows only those particles involved in the reaction and is balanced with respect to both __________ and ____________.
You can predict the formation of a ______________ by using the general rules for solubility of ionic compounds.

20. Complete Ionic Equations
A complete ionic equation is an equation that shows dissolved ionic compounds as _________________ free ions.

21. Net Ionic Equations
An ______ that appears on both sides of an equation and is not directly involved (is ______________) in the reaction is called a _______________ ion.
The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change.

22. Net Ionic Equations
Example: Sodium ions and nitrate ions are _______ changed during the chemical reaction of silver nitrate and sodium chloride so the net ionic equation is

23. Predicting the Formation of a Precipitate
You can predict the formation of a precipitate by using the general rules for _______________ of ionic compounds.

24. Precipitate Example
Will a precipitate form when a sodium carbonate solution is mixed with a barium nitrate solution?
Sodium nitrate is _____________ but barium carbonate is insoluble. Therefore we would write the net ionic equation as follows.

25. Chemical Changes
A chemical change is also called a chemical ______________.
One or more substances change into one or more new substances during a chemical reaction.
A substance present at the ____________ of the reaction is a _________________.
A substance produced in the reaction is a ______________.

26. Chemical Changes Possible clues to chemical change include:
a transfer of _____________
a ____________ in color
the production of a _______
the formation of a precipitate
A precipitate is a __________ that forms and settles out of a ______________ mixture.

27. Conservation of Mass
During any chemical reaction, the mass of the products is ____________ equal to the mass of the reactants.
The law of conservation of mass states that in any physical change or chemical reaction, ____________ is conserved.