Chemical Reactions and Conservation of Mass

A chemical reaction can be represented by a WORD EQUATION.

Example:Hydrogen gas + Oxygen gas Water

Reactants:the starting materials

Products:The ending materials

Test Reaction:Iron (III) nitrate + sodium iron (III) hydroxide + sodium hydroxide nitrate

1. Place reactants in CLOSED (sealed) flask. 2. Measure mass before reacting.3. Measure mass after reacting.

How will the mass of the reactants in a chemical reaction compare with the mass of products?

Why is it important that the container be closed?So no materials can escape or be added to the system!

Question:

Procedure:.

DEMONSRATION: Allow chemicals to react in a CLOSED container

Initial Mass before reaction: (g) Predicted Mass after reaction: (g)

Measured Mass after reaction: (g) Explanation:

Prediction and Observation:

Summary: The mass before and after the reaction is the same.

This is because the number of atoms stays the same. The atoms are rearranged but are NOT created or destroyed!

Law of Conservation of Mass

In a chemical reaction, the mass of the reactants is equal to the mass of the products. Applying Conservation of Mass : How many grams of oxygen reacts with 40 g of calcium oxide to produce 100 g of calcium oxide?

Calcium + Oxygen → Calcium Oxide 40 g ? 100 g

Ans: Mass of oxygen = 100 g – 40 g = 60 g

A CHEMICAL EQUATION uses chemical symbols to represent a reaction:

Hydrogen gas + Oxygen gas Water

H2 + O2 H2O This is called a skeleton equation- the number of atoms on either side are not balanced!

H2 + O2 H2O

To balance the equation, we need to add balancing coefficients in front ofthe terms!

Atom Left Side Right Side Balanced ?

H

O2 2

2 1

2

244

2