Bell Work

• Convert the following to a chemical equation.

• Iron (III) chloride reacts with magnesium phosphate to form magnesium chloride and iron (III) phosphate.

Physical Science – Lecture 46

Intro to Balancing Chemical Equations

Chemical Equations

• In a chemical equation, there are certain numbers of elements on the reactant side and on the product side.

Law of Conservation of Mass

• Law of Conservation of Mass says that in a chemical reaction, the mass of the products equals the mass of the reactants.

• This is true because mass cannot be created or destroyed.

What does this mean for Chemical Equations?

What does this mean for Chemical Equations?

• The number of each element (not compound) on each side must be equal since mass cannot be created or destroyed.

How do we count elements in equations?

How do we count elements in equations?

• Multiply the coefficient times the subscript for each element in a chemical formula.

• If the chemical formula has parenthesis, the subscript outside the parenthesis is also multiplied by all elements inside the parenthesis.

Example

• CO2

Example

• Mg3(PO4)2

Practice

• CH3COOH

Practice

• (NH4)2CO3

Example with Coefficients

• 2 NaCl

Example with Coefficients

• 6 Mn2O3

Example with Coefficients

• 4 Be3(PO4)2

Practice

• 3 BeF2

Practice

• 3 LiNO3

Practice

• 2 Ca3(PO4)2

Balancing an Equation Rules

• Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation.

How to Balance an Equation

• Draw a chart with elements from the reactant side on the left and elements from the product side on the right.

How to Balance an Equation

• Multiply each element by any number that will make the two sides (reactant and product) equal.

How to Balance an Equation

• When multiplying, if an elements is in the same chemical formula as another, you must also multiply that element by the same number.

How to Balance an Equation

• If one element appears in more than one formula, place the element in two separate blocks and add the total number of them together.

How to Balance an Equation

• Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

Tip

• Start by balancing an element that appears in only one reactant and product.

Bell Work Example – Is it Balanced?

• 2 FeCl3 + Mg3(PO4)2 --> 3 MgCl2 + 2 FePO4

Example – Is it Balanced?

• 1 AgNO3 + 1 LiOH --> 1 AgOH + 1 LiNO3

Example – Balancing an Equation

• Find the missing number to balance the equation:

• 2 FeCl3 + 1 Be3(PO4)2 --> ___ BeCl2 + 2 FePO4

Practice – Balancing an Equation

• Find the missing number to balance the equation:

• ___ CH4+ 2 O2 --> 1 CO2 + 2 H2O

Practice – Balance the Equation

• Find the missing number to balance the equation:

• 3 Mg + 1 Mn2O3 --> ___ MgO + 2 Mn

Practice – Balance the Equation

• Find the missing number to balance the equation:

• 2 AlBr3 + 3 Ca(NO3)2 --> 3 CaBr2 + ___ Al(NO3)3