Section 8-1Describing Chemical Reactions

Chemical Reactions

• Watch closely• Record all

indications of a chemical reaction.

Write a word equation…

• Silver nitrate reacts with sodium chloride dissolved in water to form silver chloride and sodium nitrate

Silver nitrate + sodium chloride silver chloride + sodium nitrate

Now a formula equation…

• Silver nitrate reacts with sodium chloride dissolved in water to form silver chloride and sodium nitrate

Silver nitrate + sodium chloride silver chloride + sodium nitrate

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

Chemical Reactions

• Watch closely• Record all

indications of a chemical reaction.

Try writing a word equation• potassium metal

reacts with water to produce aqueous potassium hydroxide and hydrogen gas.

Potassium + water potassium hydroxide + hydrogen

Now a formula equation…• potassium metal

reacts with water to produce aqueous potassium hydroxide and hydrogen gas.

Potassium + water potassium hydroxide + hydrogen

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

Chemical Reactions

• Watch closely• Record all

indications of a chemical reaction.

(NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + 4H2O(g)Δ

Start with a word equation…• The reactant,

Ammonium dichromate is heated to yield the products nitrogen, chromium(III) oxide, and water

Ammonium dichromate nitrogen + chromium(III) oxide + water

Δ

Turn the word equation into a formula equation…

• The reactant, Ammonium dichromate is heated to yield the products nitrogen, chromium(III) oxide, and water

(NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + H2O(g)Δ

Turn the word equation into a formula equation…

• Our formula equation states the facts, and gives the correct chemical formulas for the reactants and products.

• What are we missing?

(NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + H2O(g)Δ

All Equations Can Be Translated Into A Sentence

2HgO(s) → 2Hg(l) + O2(g)

When heated, solid mercury (II) oxide yieldsliquid mercury and oxygen gas.

Example #1

• Solid sodium combines with chlorine gas to produce solid sodium chloride.

Example #2

• When solid copper reacts with aqueous silver nitrate, the products are aqueous copper (II) nitrate and solid silver.

Example #3

• In a blast furnace, the reaction between solid iron (III) oxide and carbon monoxide gas produces solid iron and carbon dioxide gas.