Chemistry Quiz #4

What is a chemical equation?

A symbolic representation of a chemical reacation showing reactants and products.

Coefficient

A number placed before a chemical formula in an equation to balance the reaction.

Subscript

A small number in a chemical formula indicating the number of atoms of an element in a molecule.

Synthesis (Combination) Reaction

A reaction where two or more substances combine to form one product.

A + B → AB

Decomposition Reaction

A reaction where one compound breaks down into two or more simpler substances.

AB → A + B

Single Replacement Reaction

A reaction where one element replaces another in a compound.

A + BC → AC + B

Double Replacement Reaction

A reaction where the ions of two compounds exchange places to form new compounds.

AB + CD → AD + CB

Precipitation Reaction

Two aqueous reactants form a solid product. 

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

Acid-Base Reaction

A proton (H⁺) and a hydroxide ion (OH^-) come together to form water (H₂O)

HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

Oxidation-Reduction Reaction (REDOX)

A chemical reaction involving the transfer of electrons; includes oxidation and reduction.

or

An exchange of electrons, which changes the oxidation state of atoms.

Na (s) + Cl (g) → NaCl (s)

Combustion Reaction

Substance combines with molecular oxygen to make oxygen compounds of other elements.

C₃H₈ (g) + 5 O₂ (g) → 3 CO₂ (g) + H₂O (g)

Photochemical Reaction

Reactions that take light to proceed comes up in organic chemistry, biochemistry and biology

Chelation Reactions

Complexes of metal ions, inorganic chemistry topic, but important in biochemistry

Solid-State Reactions

Reactions between two solids

Interface Reactions

Reactions that occur at the interface between two phases, like gas/liquid or solid/liquid or solid/gas

Aqueous (aq)

A substance dissolved in water.

Mole

A counting unit in chemistry equal to 6.022 × 10²³ particles.

• Used as conversion factor

Stoichiometry

The numerical relationship between chemicals in a reaction
• Literal meaning is “measure of element”

Polyatomic Ion

A charged particle composed of two or more atoms covalently bonded together that acts as a single ion with an overall positive or negative charge.

Oxidation

Loss of electron(s) by a reactant; by itself an oxidation half-reaction

Ex:

• Na → Na⁺ + e-

• H₂ → 2H⁺ + 2e-

• Fe²⁺ → Fe³⁺ + e-

Reduction

Gain of electron(s) by a reactant; named as gaining electron reduces charge on atom; by itself an reduction half-reaction

• Cl₂ + 2e- → 2Cl-

• O₂ + 4e⁻ → 2O²⁻

• F₂ + 2e⁻ → 2F-

• Fe³⁺ + e⁻ → Fe²⁺

Reducing Agent

a substance being oxidized causing reduction of another substance; or substance that is losing electrons

• look for the reactant that increases its oxidation number

Oxidizing Agent

a substance being reduced causing oxidation of another substance; or substance gaining electrons

• look for the reactant that lowers its oxidation number

How to Balance Redox Reactions?

1. Write skeleton equation
2. Divide the equation into half-reactions
3. Balance the half-reactions
4. Make the electrons gain equal electron loss
5. Add half-reactions
6. Cancel anything that is the same on both sides and reduce coefficients if possible

How to Balance Chemical Equations

1. Determine the correct chemical formulas for each reactant and product
2. Write the skeleton equation
3. Count the number of atoms of each element that appears as a reactant and as a product
          a) If a polyatomic is unchanged on both sides, count it as a unit
4. Balance each element one at time by placing coefficient in front of the formula
a) Start with most complex substance, the one with the most different atoms
b) Alternate between balancing reactants and products
c) Balance hydrogen and oxygen last
5. Check each or polyatomic ion to be sure that they are equal on both sides
6. Make sure all coefficients are in the lowest possible ratio, reduce if need be