Chemistry Notes 11/17

Introduction to Chemical Equations

What is a chemical reaction?

• A chemical reaction occurs any time we have a rearrangement of the ways in which atoms are grouped.

• Since we cannot directly observe this rearrangement (atoms and compounds are too small), we need to look for evidence of the chemical change…

Evidence of a chemical reaction

Evidence for a chemical reaction

• Color change (except from dilution or color mixing)

• Temperature change (except when caused by external heating or cooling)

• Formation/release of a gas (except due to physical changes such as boiling)

• Formation of a solid precipitate when mixing two liquid solutions

How do we represent a chemical reaction?

reactants products

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reaction

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reactionProducts: chemicals formed by the reaction

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reactionProducts: chemicals formed by the reactionArrow (): shows direction of change; read as

“yields” or “produces”

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reactionProducts: chemicals formed by the reactionArrow (): shows direction of change; read as

“yields or produces”

EXAMPLE: the reaction equation for methane and oxygen would be:

CH4 + O2 CO2 + H2O

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reactionProducts: chemicals formed by the reactionArrow (): shows direction of change; read as

“yields or produces”

EXAMPLE: the reaction equation for methane and oxygen would be:

carbon methane oxygen dioxide water

CH4 + O2 CO2 + H2O

How do we represent a chemical reaction?

reactants productsReactants: chemicals present before the reactionProducts: chemicals formed by the reactionArrow (): shows direction of change; read as “yields or

produces”

EXAMPLE: the reaction equation for methane and oxygen would be:

carbon methane oxygen dioxide water

CH4 + O2 CO2 + H2O reactants products

Special symbols

• (l) The chemical is a liquid.

Special symbols

• (l) The chemical is a liquid.• (s) The chemical is a solid.

Special symbols

• (l) The chemical is a liquid.• (s) The chemical is a solid.• (g) The chemical is a gas.

Special symbols

• (l) The chemical is a liquid.• (s) The chemical is a solid.• (g) The chemical is a gas.• (aq) The chemical is aqueous (dissolved in

water).

Special symbols

• (l) The chemical is a liquid.• (s) The chemical is a solid.• (g) The chemical is a gas.• (aq) The chemical is aqueous (dissolved in

water).• Δ: written above an arrow, it indicates that

heat needs to be added to the reagents for them to react.

Special symbols• (l) The chemical is a liquid.• (s) The chemical is a solid.• (g) The chemical is a gas.• (aq) The chemical is aqueous (dissolved in

water).• Δ: written above an arrow, it indicates that heat

needs to be added to the reagents for them to react.

• CH4 (g) + O2 (g) CO2 (g) + H2O (l)

Examples/Practice• Write a chemical equation for the following

reactions:

1. Solid mercury (II) oxide decomposes to produce liquid mercury metal and gaseous oxygen.

2. Solid zinc is added to an aqueous solution containing dissolved hydrogen chloride to produce gaseous hydrogen and zinc chloride dissolved in water

Classwork/Homework

• In textbook on p. 166-167: #7-12, 15, 22