Balancing Equations and Classifying Chemical Reactions What are the parts of a chemical equation? What do these parts represent? Why do we balance chemical equations? How do we balance chemical equations? How can we use a chemical equation to identify the type of chemical reactions?

What are the parts of a chemical equation? Let’s examine this chemical equation and learn what each part means: 2H2 + O2 → 2H2O Identify: Reactants products subscript coefficient

2H2 + O2 → 2H2O How are reactants and products related? Reactants are the materials you start a reaction with and the products are the materials you end with.

2H2 + O2 → 2H2O How is a subscript different from a coefficient? A subscript is lower and smaller and follows an element’s symbol. It represents the number of atoms of that element in a molecule or compound. (O2) A coefficient is the number in front of a chemical formula and it shows the number of molecules. (Just like in math, a coefficient multiplies the term it’s attached to ) (2 H2O)

2H2 + O2 → 2H2O How is a chemical equation different from This is a formula How is a chemical equation different from a chemical formula? A chemical equation shows an entire chemical reaction in symbol form A chemical formula is a combination of symbols and subscripts that represent the numbers and kinds of elements in a compound. This entire thing is an equation

Analyze the following: N2 + 3H2  2NH3 What are the reactants? Product(s) How many atoms of N are present in the reactants? Products? How many atoms of H are present in the reactants? Products?

Analyze the following 2CuO + C  2Cu + CO2 What are the reactants? Product(s) How many atoms of each element are present in the reactants? Products?

Analyze the following H2 + Cl2  HCl What are the reactants? Product(s)? How many atoms of H are present in the reactants? Products? How many atoms of Cl are present in the reactants? Products? Do you see a difference between the analysis of this equation and the previous two?

Balancing Chemical Equations H2 + O2  2H2O

Balancing Chemical Equations Law of Conservation of Matter: Matter cannot be created or destroyed, it can only be transformed When writing chemical equations, the law of conservation of mass is observed: This means that the numbers of atoms of each element must be the same on each side of the equation In equation 1 and 2, the numbers of each type of element were the same in reactants and products. In equation 3 they aren’t.

Balancing Chemical Equations We balance equations to account for and accommodate the Law of Conservation of Matter. We’ve learned in the previous unit that the CHEMICAL FORMULA is determined by electron configuration and obeys the Law of Conservation of Charge. Because of that, we can’t just change subscripts to show Law of Conservation of Matter. We must use coefficients.

Balancing Chemical Equations Example A N2 + H2  NH3 Example B NaCl + F2  NaF + Cl2

Balancing Chemical Equations Practice: P + O2  P2O5 Na + H2O  NaOH + H2 HCl + CaCO3  CaCl2 + H2O + CO2

Steps for Balancing Chemical Equations “Take Inventory” Count the numbers of atoms of each element in each side of the equation Choose which side to start Adjust coefficient of molecule and adjust the inventory Repeat until the numbers of each type of atoms on each side matches NEVER EVER EVER EVER CHANGE A SUBSCRIPT NEVER EVER EVER INSERT A COEFFICIENT IN THE MIDDLE OF A FORMULA PRACTICE, PRACTICE, PRACTICE

Classifying Chemical Reactions 1. Synthesis 2 or more substances combine 2SO2 + O2 + 2H2O  2H2SO4 (A + B + C  ABC) 2. Decomposition breaking down compounds 2H2O2  2H2O + O2 (AB  A + B) 3. Single Replacement single - 1 element replaces another in a compound 2CuO + C  2Cu + CO2 (AB + C  A + BC) 4.Double Replacement double - 2 elements in different compounds trade places RbBr + AgCl  AgBr + RbCl (AB + CD  CB + AD) 5. Combustion hydrocarbon (fuel) plus oxygen yields carbon dioxide plus water

Balance and classify the following chemical reactions ____ Na +____ I2  ____ NaI ____ KClO3  ____ KCl + ____ O2 ____Na + ____ HCl  ____ NaCl + ___ H2 ____ K3PO4 + ____ HCl  ____ KCl + ____ H3PO4 ____ C3H8 + ____ O2  ____ CO2 + ____ H2O