CHAPTER 8

Section 1

Chemical Reaction – the process by which one or more substances are changed into one or more different substances

Reactants – the original substancesProducts – the resulting substancesChemical Equation – represents with

symbols and formulas the identity of the substances and the relative amounts of the reactants and products in a chemical reaction.

Indications of a Chemical Reaction

Heat and LightMatch

Gas producedHC2H3O2 and NaHCO3

Formation of a PrecipitatePrecipitate (ppt) – a solid produced in a

chemical reactionNaCl and AgNO3

Color ChangeNaOH and Phenolphthalein

Characteristics of Chemical Equations

The equation must represent known facts

The equation must contain correct formulas for reactants and products

The law of conservation of mass must be satisfiedCoefficient – a small whole number that appears in front

of a formula in a chemical equation

Equations

Word Equation- an equation in which the products and reactants in a chemical reaction are represented by words

Methane + oxygen → carbon dioxide + water

→ - yields, produce, or form

Equations

Formula equation – represents the reactants and products of a chemical reaction by their symbols or formulas

CH4(g) + O2(g) → CO2(g) + H2O(g)

(g) represents state

→ - yields↔ - reversible rxn(s) - solid(g) - gas(l) - liquid(aq) - aqueous (dissolved in water)→ - rxn heated, other specific conditions

examples

Symbols

Δ

Law of Conservation of Mass and Formula Equations

CH4(g) + O2(g) → CO2(g) + H2O(g) not balanced

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) balanced

Practice

CS2(l) + O2(g) → CO2(g) + SO2(g)

NaCl(aq) + AgNO3(aq) →NaNO3(aq) + AgCl(s)

PbCl2(aq)+Na2CrO4(aq) → PbCrO4(s) +NaCl(aq)

Practice

CS2(l) + 3O2(g) → CO2(g) + 2SO2(g)

NaCl(aq) + AgNO3(aq) →NaNO3(aq) + AgCl(s)

PbCl2(aq) + Na2CrO4(aq) → PbCrO4(s) + 2NaCl(aq)

Balancing equations

Write formula equations – make sure you have correct formulas

Balance elements that appear only once on each side

Balance polyatomic ions as single units (in most cases)

Balance H and O last

Examples

Examples

Magnesium and hydrochloric acid react to produce magnesium chloride and hydrogen.

Nitric acid reacts with magnesium hydroxide to produce magnesium nitrate and water

When copper reacts with silver nitrate, the products are copper(II) nitrate and silver

The reaction between iron(III) oxide and carbon monoxide gas produces iron and carbon dioxide.

Practice

Solid calcium reacts with solid sulfur to produce solid calcium sulfide

Hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas

Solid aluminum metal reacts with aqueous zinc chloride to produce solid zinc metal and aqueous aluminum chloride