Balancing Chemical Equations Types of Reactions Chemical reactions

Balancing Chemical Equations Types of Reactions

Chemical reactions Chemical reaction: is a process in which one or more substances are converted into new substances with different physical and chemical properties. 2 types of substances in a chem rxn. Reactant: present before the reaction Product: what is made by the rxn

Chemical equations These represent chemical reactions in sentence form. These describe exactly what is happening in a rxn and tells us what is the reactant and what is the product. Word equations Uses the names of the reactants and products Ex. Calcium reacts with Oxygen to yield calcium oxide

Formula equations This is more common Here the above reaction would be written as: Ca + O 2 Ca. O + means reacts with means yields The key here is to make sure you use the correct symbols for the reactants and products.

Balancing chemical reactions Law of conservation of matter: Matter can neither be created or destroyed just changed tells you that the amount of matter or atoms in the reactant side must equal the product side. When this occurs it is called a balanced chemical reaction

Go back to : Ca + O 2 Ca. O Is this balanced? Coefficients: these are whole numbers written before a chemical symbol. Diatomic Molecules: elements that are never alone in nature. Come in pairs Ex. O 2 HONCl. Br. IF

Ca + O 2 Ca. O So in the above rxn how many O are on the reactant and product sides respectively? 2: 1 How many Ca? 1: 1 With the use of coefficients we can make both sides have 2 O’s. Ca + O 2 2 Ca. O We now have 2 O’s on both sides but what about the Ca now? Add a 2 to Ca: 2 Ca + 02 2 Ca. O Is this balanced now?

Try this problem Methane (CH 4) + oxygen gas carbon dioxide + water Complete chemical equations • When you balance an equation you are telling us how exactly the atoms are going to be. • Another thing you need to tell us then is what state of matter they are in. • You do this by putting a letter to designate the state of matter behind the symbol of the chemical. Ex. CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l)

Evidence of a chemical reaction 1. Color Change 2. Gas release (bubbles) 3. Heat change or light release 4. Precipitate formed

5 Types of reactions 1. Combination (synthesis) • Like a combination pizza Generic terms: A + B AB or AB + C ABC Example: 2 Na + Cl 2 2 Na. Cl Key: only 1 product will be formed You try: Potassium reacts with Chlorine gas Answer: 2 K + Cl 2 2 KCl

2. Decomposition Like a dead body eventually does Generic terms: AB A + B or ABC A + BC Example 2 H 2 O 2 H 2 + O 2 Key: only 1 reactant will be there You try: Sulfur Dichloride decomposes into Answer: SCl 2 S + Cl 2

3. Combustion reaction * similar to a combination but can make more than one product * Key: Oxygen gas is always a reactant Generic terms: A + O 2 AO or AB + O 2 AO + BO Example: 2 Mg + O 2 2 Mg. O Hydrocarbons: molecules made of only Hydrogen and Carbons (sometimes some oxygen) These always make 2 products: CO 2 and H 2 O

You try: Dicarbon Hexahydride combusts with oxygen gas Answer: 2 C 2 H 6 + 7 O 2 4 CO 2 + 6 H 2 O * If problem says “combusts” that mean O 2 is a reactant!

4. Single replacement reaction: Freshman reaction Generic Terms: AB + X AX + B Example: Mg. Cl 2 + K KCl + Mg * Key: there is always a single element and a compound on reactant side. *Metals activities series: tells which metals are stronger, if single element is not stronger then NO REACTION You try: Magnesium metal reacts with Hydrochloric Acid Answer: Mg + 2 HCl Mg. Cl 2 + H 2

5. Double displacement reaction: The clique rxn Generic terms: AX + BY AY + BX Example: Cu. SO 4 + 2 Li. Cl Cu. Cl 2 + Li 2 SO 4 • Key: there are 2 compounds as reactants and 2 compounds as products • Often a precipitate will form: solid from 2 clear liquids You try: Barium Sulfide reacts with Nickel (II) Iodide Answer: Ba. S + Ni. I 2 Ba. I 2 + Ni. S