Chapter 6: Chemical Reactions: An Introduction

Section 6.1: Evidence for a Chemical ReactionSection 6.2: Chemical EquationsSection 6.3: Balancing Chemical Equations

6.1: Evidence for a Chemical Reaction

Objective: To learn the signals that show a chemical reaction has occurred.

Steel (smooth, shiny) to rust (reddish-brown, flaky)Hair changes color when its bleachedNylon is formed from 2 liquids

Blue flame is seen when naturalGas combines with oxygen

Unexpected reactions

Ammonia + Bleach give chloramines toxic gasesDemonstration of a chemical reaction

6.2: Chemical Equations

Objective: To learn to identify the characteristics of a chemical reaction and the information given by a chemical equation.

CHEMICAL Reaction: chemical changeChemical Equation: representation of achemical reaction.Reactants Products

Methane + Oxygen Carbon Dioxide + Water

CH4 + O2 CO2 H2O

Chemical reaction involves changing theways the atoms are grouped.

Atoms are not created or destroyed.

All atoms are present in the reactantsMust be accounted for in the products.

BALANCING THE CHEMICAL REACTIONObeys this rule.

CH4 + O2 CO2 + H2O

C H HH H

O O C O OH HO

C H HH H

O O C O OH HO

O OH HO

CH4 + 2O2 CO2 + 2H2O

The chemical equation for a reaction provides

1)The identities of the reactants and products2)The relative numbers of each

Physical States

Symbol State

(s) Solid

(l) Liquid

(g) Gas

(aq) dissolved in water(in aqueous solution)

6.3: Balancing Chemical Equations

Objective: To learn how to write a balanced equation for a chemical reaction

Balancing a Chemical Reaction

• Atoms are conserved in a chemical reaction

• The identities (formulas) of the compound must never be changed in balancing a chemical equation.

• Coefficients: integers used to balance an

Equation.

Balancing a Chemical Reaction

• Liquid ethanol (C2H5OH) reacts with gaseous oxygen to produce gaseous carbon dioxide and gaseous water.

Step 1:

C2H5OH(l) + O2(g) CO2(g) + H2O(g)

Step 3 and Step 4:

C2H5OH(l) + 3O2(g) 2CO2(g) + 3H2O(g)

Balancing a Chemical Reaction

• Solid potassium reacts with liquid water to form gaseous hydrogen and potassium hydroxide that dissolves in the water.

Step 1:

K(s) + H2O(l) H2(g) + KOH(aq)

2K(s) + H2O(l) H2(g) +2KOH(aq)

Balancing a Chemical Reaction

• Ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide (nitric oxide) and gaseous water.

Step 1:

NH3(g) + O2(g) NO(g) + H2O(g)

4NH3(g) +5O2(g) 4NO(g) +6H2O(g)