1.4 Chemical Reactions

In a chemical equation, on which side do you put the reactants and the products?

• Reactants on the left side

• Products on the right side

What is the chemical equation of Hydrogen and Oxygen becoming water?

• 2H_2(g) + O_2(g) → 2H₂O_(l)

How do you know how many atoms are in an molecule?

• Look at the _subscript

How many atoms of Hydrogen and Oxygen are in these reactants: 2H_2(g) + O_2(g)

• Two Hydrogens meaning there are four atoms

• One Oxygen meaning there are two atoms

• Six atoms in total

If there are 6 atoms in the reactants to become water, how many atoms must water have? What is this called?

• Must have six

• Law of conservation of mass

Define Law of Conservation of Mass

• Matter is neither created nor destroyed in a chemical reaction

• Means that the mass of any chemical process is a constant

When the reactant side has the same number and kinds of atoms as the product side, this chemical equation is called what?

• A balanced chemical equation

In a balanced equation, besides the molecules and atoms, what else does it require?

• The appropriate states of each element or compound

What are the subscript letters these states: solid, precipitate, liquid, dissolved in water/aqueous, gas

• s

• s

• l

• aq

• g

Is the total number of molecules the same on each side of a balanced equation?

• No

Is the total number of atoms the same on each side of a balanced equation?

• Yes

Define the 5 step strategy for balancing chemical equations

1. Make a table to summarize how many atoms of each element you have on the reactant side and the product side

2. Identify elements or polyatomic ions that need to be balanced

3. Add a whole number to the front of the chemical formula

4. Apply that change to all the atoms in the formula and update the table

5. Continue to identify elements that need to be balanced and write the appropriate whole number in the reaction then apply the change and update the table

When each type of atom is equal in number on both sides of the chemical reaction you have balanced the reaction!

Most reaction are balanced using only _____

• Small whole numbers

Name the 5 types of chemical reactions

1. Synthesis reactions

2. Decomposition reactions

3. Combustion reactions

4. Single displacement reactions

5. Double displacement reactions

What type of reaction is this?

• Combustion

What type of reaction is this?

• Decomposition reaction

What type of reaction is this?

• Single displacement reaction

What type of reaction is this?

• Synthesis reaction

What type of reaction is this?

• Double displacement reaction

Define synthesis reaction. What is the equation in simple letters?

• When two or more reactants combine to form a single new compound

• A + B → AB

• *Only one product is ever formed

Define decomposition reaction. What is the equation in simple letters?

• Opposite of synthesis

• Involves the breakdown of a large complex compound into smaller, simply elements or compounds

• AB → A + B

Define combustion reaction

• “Combustion” means the burning of a substance

• Usually, a fuel source reacts with Oxygen to produce heat and other products

Define single displacement reaction. What is the equation in simple letters?

• Occurs when one element displaces the same type of element in a compound

• A + BC → B + AC

• Single element replaces whatever element in the compound it is most similar to

• ex: a metal will take the place of a metal; a non-metal will take the place of a non-metal

Define double displacement reaction. What is the equation in simple letters?

• Occurs when an element from a compound displaces another element from a different compound

• AB + CD → AD + CB

• First parts go with second parts; everything switch but stays in the same spot as before