5. Chemical Reactions & Stoichiometry

Question 1

Chemical Reaction

Answer 1

• reactants –> products
• chemical bonds between atoms in the reactants are broken and new bonds are formed in different combinations to form products

Question 2

Decomposition

Answer 2

• chemical reaction whereby larger reactants are broken down into smaller products

AB –> A + B

Question 3

Catabolism

Answer 3

• particular form of decomposition
• biochemical process of breaking down molecules to supply energy

proteins–> amino acids

proteins –> glucose

glycogen –> glucose

triglycerides –> fatty acids

Question 4

Combination

Answer 4

• chemical reaction whereby smaller reactants combine to form larger products

A + B –> AB

Question 5

Anabolism

Answer 5

• particular form of combination reaction
• biochemical process of building larger molecules from smaller ones, such as the synthesis of stuctural components of cells and tissues

Question 6

Single Replacement Reaction

Answer 6

• involves two reactants and two products, whereby an atom or molecule within a compound is replaced by another atom or molecule

AB + C –> AC + B

Question 7

Double Replacement Reaction

Answer 7

• involves two reactants and two products, whereby two substances exchange parts with one another to form two different substances

AB + CD –> AC + BD

• ‘partner switching’

Question 8

Dissociation

Answer 8

• ionic compounds dissolve in water to form separate positive and negative ions

Question 9

Aqueuos Solution

Answer 9

• solution in which the solvent is water

Question 10

Spectator Ions

Answer 10

• an ion that appears unchanged on both sides of a chemical equation

Question 11

Net Ionic Equation

Answer 11

• chemical equation that does not show spectator ions

Question 12

Ions in solution react with each other when either:

Answer 12

• two ions form a solid that is insoluble in water
• two ions form a gas
• an acid neutralizes a base to form water
• one ion oxidises another

Question 13

Redox Reaction

Answer 13

• oxidation - reduction reaction which involves the transfer of electrons from one species to another
• oxidation and reduction are complimentary processes ie. one cannot occur without the other

Question 14

Oxidation

Answer 14

• loss of electrons
• gain of oxygen atoms and/or the loss of hydrogen atoms

Question 15

Reduction

Answer 15

• gain of electrons
• loss of oxygen atoms and/or the gain of hydrogen atoms

Question 16

Oxidising Agent

Answer 16

• entity that accepts electrons in a redox reaction
• substance that is reduced
• chemical species which causes another species to undergo oxidation

Question 17

Reducing Agent

Answer 17

• entity that donates electrons in a redox reaction
• substance that is oxidised
• chemical species which causes another species to undergo reduction

Question 18

Combustion

Answer 18

• particular type of redox reaction involving the production of heat and light

Question 19

Respiration

Answer 19

• particular type of redox reaction equivalent to combustion, except that it takes place more slowly + at a much lower temperature
• humans + animals acquire energy by respiration by oxidising carbon-containing componds in cells with the air breathed to produce carbon dioxide, water + energy

Question 20

Rusting

Answer 20

• iron is oxidised to a mixture of iron oxides

Question 21

Bleaching

Answer 21

• common bleaches are oxidising agents
• coloured compounds being bleached are usually organic + are converted to colourless compounds by oxidation

Question 22

Voltaic Cells

Answer 22

• device in which electricity is generated from a chemical reaction
• also known as a battery
• electrons produced at the negative electrode (anode) are consumed at the positively charged electrode (cathode)

Question 23

Heat of Reaction

Answer 23

• heat given off or absorbed during a chemical reaction

Question 24

Exothermic

Answer 24

• reaction that gives off heat

Question 25

Endothermic

Answer 25

• reaction that absorbs heat

Question 26

Heat of Combustion

Answer 26

• heat given off in a combustion reaction
• all combustions are exothermic

Question 27

Exergonic Reactions………..

Answer 27

……….generate energy

Question 28

Endergonic Reactions……….

Answer 28

……….absorb energy

Question 29

Free Energy

Answer 29

• the chemical energy of a substance

Question 30

Side Reaction

Answer 30

• secondary or subsidiary reaction that takes place simultaneously with the reaction of primary interest

Question 31

Stoichiometry

Answer 31

• term that applies to the quantative aspects of chemical composition + chemical reactions

Question 32

Formula Weight

Answer 32

• sum of the atomic weights of all the atoms in one formula unit

Question 33

Molecular Weight

Answer 33

• sum of the atomic weights of all the atoms in a molecule

Question 34

Mole

Answer 34

• quantity of a substance whose mass in grams is numerically equal to the substances formula weight

Question 35

Avogadro’s number

Answer 35

• 6.02 x 10²³
• number of formula units per mole

Question 36

Molar Mass

Answer 36

• mass of one mole of a substance expressed in grams
• formula weight of a compound expressed in grams

Question 37

Limiting Reagent

Answer 37

• reactant that is consumed leaving an excess of another reagent or reagents unreacted

Question 38

Actual Yield

Answer 38

• mass of product actually obtained from a particular chemical reaction

Question 39

Theoretical Yield

Answer 39

• maximum amount of product that could be obtained from a particular mixture of reactants

Question 40

Percent Yield

Answer 40

% yield = (actual yield / theoretical yield) x 100

Question 41

Oxidation State (Number)

Answer 41

• indicates the number of electrons lost, gained or shared as a result of chemical bonding
• change in oxidation state of a species indicates whether it has undergone oxidation or reduction
• oxidation involves an increase in oxidation number
• reduction involves a decrease in oxidation number ie. reduction of charge
• the more electronegative element in a substance will have a negative oxidation number, while the less electronegative element will have a positive oxidation number
• alkali metals are always +1
• alkaline earth metals are always +2
• oxygen is -2, for peroxides -1 and F₂O +2
• flourine is always -1
• chlorine is -1, except with O or F
• hydrogen is +1, except with metal hydrides where it is -1