Unit 6: Reactions

Question 1

chemical equation

Answer 1

Communicates what types and how many molecules are involved in a reaction (symbolic representation of a chemical reaction)

Question 2

How do you balance a chemical equation?

Answer 2

The number of atoms of each element in the reactants must be the same as in the products

Only change the coefficients; NEVER the subscripts

Tips for balancing:

• Begin by balancing the elements in the most complex formula
• If it is possible, group polyatomic ions together and balance them separately from their elements

Question 3

chemical reaction

Answer 3

Occurs when compounds break their bonds and form new compounds with new bonds

Question 4

reactants

Answer 4

Compounds present before the chemical reaction

Question 5

products

Answer 5

Compounds present after the chemical reaction

Question 6

How can you identify a decomposition chemical reaction?

Answer 6

Often occur when ionic compounds are heated; outcome is not always straightforward although there are patterns — usually they are common, stable, small molecules, especially gases. If a gas can form as a product, it nearly always does. (Other patterns attached)

Reactants: 1 compound

Products: 2 elements (or smaller compounds)

EX: CD → C + D

Question 7

How can you identify a combination chemical reaction?

Answer 7

AKA synthesis

Often occur when two elements are heated; outcome can often be predicted by considering the most stable ionic charge of both species

Reactants: 2 elements or compounds

Products: 1 compound

EX: A + B → AB

Question 8

How can you identify a neutralization chemical reaction?

Answer 8

Occurs between an acid and a base to produce a salt and water

Reactants: HX + BOH

Products: BX + H₂O + Δ

An Arrhenius acid (HX) is a proton donor (H+)

An Arrhenius base (BOH) is a hydroxide donor (OH-)

A salt (BX) is any soluble ionic compound

Question 9

How can you identify a combustion chemical reaction?

Answer 9

Occur when oxygen reacts with something to produce flames and heat

Reactants: M + O₂(g)

Products: MO + Δ

EX: One of the most common combustion reactions occurs between a hydrocarbon and oxygen gas to produce carbon dioxide gas and water vapor

C_nH_m + O₂(g) → CO₂(g) + H₂O(g) + Δ

Question 10

How can you identify a single-displacement chemical reaction?

Answer 10

Produce an ionic compound and a metal from a metal and an ionic compound

Reactants: 1 element and compound

Products: 1 element and compound

EX: A(s) + CD(aq) → C(s) + AD(aq)

The outcome of a single-displacement reaction is predicted by the activity series - the element that is most reactive (e.g. K) will kick the one with lower reactivity out of the compound (attached chart will be provided on test)

Hydrogen is included in the list because it has similar reactivity to metals; these reactions produce H₂ gas rather than a solid metal

Question 11

How can you identify a double-displacement chemical reaction?

Answer 11

Produce an insoluble precipitate from two soluble ionic compounds

Reactants: 2 compounds

Products: 2 compounds

EX: CD(aq) + EF(aq) → CF(aq) + ED(s)

CD, EF, CF, and ED are all ionic compounds BUT ED is insoluble in water

The outcome of a double-displacement reaction is predicted by the solubility rules - the table (attached; will be provided on test) will indicate which combo is insoluable.

Question 12

precipitate

Answer 12

An insoluble ionic compound that does not dissolve in water.

If a possible product is insoluble, a precipitation reaction shoud occur

Question 13

stoichiometry

Answer 13

Defines the relationships between the amounts of reactants and products

Question 14

mole ratio

Answer 14

ratio of the coefficients in a balanced chemical equation and acts as a unit factor

Question 15

mass to mass conversion

Answer 15

Question 16

limiting reactant

Question 17

percent yield

Answer 17

describes how close the actual yield was to the theoretical yield

= (actual / theoretical) *100

Question 18

actual yield

Answer 18

describes what one person collected after one experiment

Question 19

theoretical yield

Answer 19

describes the calculated amount of product anyone could collect for a given set of starting conditions

Question 20

ion-product constant of water

Answer 20

K_w

At 25 ºC, the value of K_w is 1.0 × 10^-14

The value of K_w cannot change (unless the temperature changes) so adding an acid to water both increases [H⁺] and decreases [OH^-]

Likewise, adding a base to water both increases [OH-] and decreases [H+]

In a neutral solution, [H+] = [OH-]

In an acidic solution, [H+] > [OH-]

In a basic solution, [OH-] > [H+]

Question 21

pH

Answer 21

The pH of a solution is defined as the negative base 10 logarithm (log) of the concentration:

pH = -log[H+]

Question 22

titration

Answer 22

Titrations involve using an acid of known concentration to determine the unknown concentration of a base

The equivalence point of a titration occurs when the moles of acid added equals the moles of base present

Question 23

precipitate calculation

Answer 23

Vol of A to Vol of B

Vol in liters of A ⇒ use Molarity to calculate moles of A ⇒ use mole ratio to get to moles of B ⇒ use Molarity to calculate Vol in liters of B

Vol of A to Mass of B

Vol in liters of A ⇒ use Molarity to calculate moles of A ⇒ use mole ratio to get to moles of B ⇒ use molar mass to calculate mass of B