3.1.1 An Introduction to Chemical Reactions and Equations

Question 1

reactions

Answer 1

• Starting materials (reactants), (products) and special conditions describing chemical changes (reactions) are expressed in concise statements called chemical equations.
• Reactions obey the law of conservation of mass.
• Reactant atoms are balanced with product atoms using integer coefficients.

Question 2

An Introduction to Chemical Reactions and Equations

Answer 2

• The plus sign (+) between reactants is read “reacts with”, and the arrow is read “to produce”.
• Stoichiometric coefficients are whole number coefficients that indicate the number of units of each reactant and product involved in a balanced equation.
• Subscripts are never changed to balance a chemical equation.
• Phases of matter (solid, liquid, gas, aqueous) give information about the physical state of the materials present as the reaction proceeds.
• A reaction arrow separates reactants from products and indicates the direction of the reaction.
• In this example, addition of two moleculesof hydrogen gas to one molecule of oxygen gas produces two molecules of liquid water.
• Equations are similar to recipes, with each reactant being an ingredient in the recipe. The reactants in the pancake example are 2 eggs, 2 cups of flour, and a cup of milk. This produces 12 pancakes. The reaction arrow represents cooking.
• In this example, iron reacts with oxygen to produce iron(III) oxide, (Fe2O3). Note that their are 4 atoms of Fe and 6 atoms of oxygen on each side of the balenced reaction.
• The equation is balanced

Question 3

Which of the following chemical equations is not a correctly balanced equation?

Answer 3

2N2 + 3H2 → 2NH3

Question 4

Which equation is balanced for the following reaction?

sodium hydroxide → sodium oxide + water

Answer 4

2NaOH → Na2O + H2O

Question 5

In the chemical equation 2Mg + O2 → MgO How must the product be written in order for the equation to be balanced?

Answer 5

2MgO

Question 6

In the following balanced chemical equation,

2Al(OH)3 + 3H2 SO4 → Al2(SO4 )3 + 6H2 O 

what is the ratio of water molecules produced per molecule of sulfuric acid in the reaction?

Answer 6

2 molecules of water per molecule of sulfuric acid

Question 7

Which one of the following chemical equations is balanced?

Answer 7

SO3 + H2O → H2SO4

Question 8

Which elements in the following chemical equation are not balanced?

2AgNO3 + H2 S → Ag2 S + HNO3

Answer 8

hydrogen, nitrogen, and oxygen

Question 9

Which of the following represents a balanced chemical equation for the word equation below?
iron(II) sulfide + hydrochloric acid → iron(II) chloride + hydrogen sulfide

Answer 9

FeS + 2HCl → FeCl2 + H2S

Question 10

Balance the following chemical equation.

Na3 PO4 + CaCl2 → Ca3(PO4 )2 + NaCl

Answer 10

2Na3 PO4 + 3CaCl2 → Ca3 (PO4 )2 + 6NaCl

Question 11

Balance the following chemical equation.

CH4 + O2 → CO2 + H2 O

Answer 11

CH4 + 2O2 → CO2 + 2H2 O

Question 12

In a balanced chemical reaction, 2 molecules of ethane (C2H6 ) react with 7 oxygen molecules (O2 ) to produce carbon dioxide (CO2 ) and water (H2O) molecules. Complete the balancing of this equation.

Answer 12

2C2H6 + 7O2 -> 4CO2 + 6H2O