Unit 4 Practice: Easy

Answer: 2H₂ + O₂ → 2H₂O

Explanation: There are 2 oxygen atoms on the left, so place a 2 in front of H₂O.

That gives 4 H atoms on the right, so place a 2 in front of H₂.

The equation is now balanced.

Answer: N₂ + 3H₂ → 2NH₃

Explanation: N₂ contains 2 nitrogen atoms, so place a 2 in front of NH₃.

Now the products contain 6 H atoms, so place a 3 in front of H₂.

Answer: An ion that does not actually participate in the chemical change.

Explanation: Spectator ions appear unchanged on both sides of a complete ionic equation.

They are removed when writing the net ionic equation.

Answer:

Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

Explanation: Ag⁺ and Cl⁻ combine to form insoluble silver chloride.

Other ions that may be present remain dissolved and are spectators.

Answer: Aqueous, meaning dissolved in water

Explanation: For example:

NaCl(aq)

means sodium chloride is dissolved in water and its ions are surrounded by water molecules.

Answer: Physical change

Explanation: The identity of the substance remains H₂O.

Only the physical state changes from solid to liquid.

Answer: Chemical change

Explanation: Methane reacts with oxygen to form new substances, mainly CO₂ and H₂O.

The chemical identities change.

Answer: The use of balanced chemical equations to calculate amounts of reactants and products.

Explanation: The coefficients in a balanced equation give mole ratios that allow one substance to be converted into another.

Answer: 2.00 mol H₂O

Explanation: The balanced equation gives:

1 mol O₂ : 2 mol H₂O

So:

1.00 mol O₂ × 2 = 2.00 mol H₂O

Answer: The reactant that is completely used up first.

Explanation: Once the limiting reactant is gone, no more product can form.

It determines the maximum theoretical yield.

Answer: The maximum amount of product predicted by stoichiometry.

Explanation: It assumes the reaction goes perfectly with no product loss and no competing reactions.

Answer:

Percent yield = (actual yield / theoretical yield) × 100%

Explanation: Actual yield comes from the experiment.

Theoretical yield comes from stoichiometric calculation.

Answer: Loss of electrons

Explanation: A species that loses electrons becomes more positively charged or less negatively charged.

Answer: Gain of electrons

Explanation: A species that gains electrons becomes more negative or less positive.

Answer:

Oxidation Is Loss

Reduction Is Gain

Explanation: It is a common way to remember electron transfer in redox reactions.

Answer: 0

Explanation: Any element in its pure elemental form has oxidation number 0.

Answer: +1

Explanation: For a monatomic ion, oxidation number equals the ion's charge.

Answer: A proton donor

Explanation: A Brønsted-Lowry acid transfers H⁺ to another species.

Answer: A proton acceptor

Explanation: A base accepts H⁺ from another species.

Answer: The point where stoichiometrically equivalent amounts of reactants have reacted.

Explanation: At equivalence, enough titrant has been added to react completely according to the balanced equation.