module 3

Question 1

what are the two types of changes

Answer 1

• physical: does not result in the formation of new substances
• chemical: involves the formation of new substances

Question 2

indicators of a physical reaction

Answer 2

• change in state
• change in size/shape
  eg. synthesis and decomposition

Question 3

indicators of a chemical change

Answer 3

• production of bubbles that indicates the a gas has been formed
• production of odour
• change in temperature
• formation of a precipitate

Question 4

what are the six types of reactions

Answer 4

• synthesis
• decomposition
• combustion (+incomplete)
• precipitation
• acid + base
• acid + carbonate

Question 5

synthesis reaction

Answer 5

reaction between two or more substances to form a new substance
- two metals –> ionic
- non-metal + metal –> covalent

Question 6

decomposition

Answer 6

where one reactant is broken into two or more constituent substances and requires the input of energy to break bonds
- thermal decomposition
- electrolysis
- photolysis

Question 7

combustion

Answer 7

• burning a substance in oxygen at high temperatures to form new products
• exothermic
• complete: fuel + oxygen –> water + carbon dioxide
• incomplete: fuel + oxygen –> water = carbon dioxide + carbon monoxide + soot (C)

Question 8

precipitation

Answer 8

mixing two solutions together resulting in the formation of a insoluble solid –> precipitate
- predicted using solubility rules
- nagsag
- care bear stroller

Question 9

acid base (neutralisation)

Answer 9

• acid + base –> salt + water
• exothermic

Question 10

acid carbonate

Answer 10

• acid + carbonate –> salt + water + carbon dioxide

Question 11

process of cycads

Answer 11

• cut up fruit and place in mesh bags
• soaked in water to leach out the toxins
• heat the fruit which causes thermal decomposition of toxins
• fruits in the mesh bags are places in a running stream of water to leach out the toxins
• fermentation to leach out the toxins

Question 12

metal and steam

Answer 12

hydrogen gas and metal oxide

Question 13

metal and water

Answer 13

metal hydroxide and hydrogen gas

Question 14

metal and oxygen

Answer 14

metal oxide

Question 15

metal and dilute acid

Answer 15

salt and hydrogen gas

Question 16

displacement reactions

Answer 16

the more reactive metal displaces the less reactive metal ions from the solution

Question 17

atomic radius

Answer 17

• increases across the group and decreases down the period
• larger atomic radius –> the zeff is lower –> easier to remove electrons –> more reactive

Question 18

ionisation energy

Answer 18

energy required to remove one valence electron from an element in the gaseous state
- increases across the period and decreases down the group
- lower first ionisation energy –> easier to remove valence electrons –> more reactive

Question 19

electronegativity

Answer 19

strength which atoms in a compound are able to attract shared electrons to itself
- increases across the period and decreases down the group
- lower electronegativity –> does not hold valence electrons well –> easier to remove valence electrons –> more reactive

Question 20

oxidation number/state

Answer 20

hypothetical charge of an atom if all bonding was ionic –> degree of oxidation

1. neutral atoms/one element = 0
2. overall oxidation state of a compound = 0
3. ions or polyatomic ions = overall charge
4. fluorine = -1
5. hydrogen = +1 (covalent) [-1 in hydrides]
6. oxygen = -2 in compounds (-1 peroxide)

Question 21

redox reaction

Answer 21

• oxidation and reduction occur
• oxidation of one or more species has changed

Question 22

oxidation

Answer 22

• increase in oxidation state
• loss of electrons
• reducing agent

Question 23

reduction

Answer 23

• decrease in oxidation state
• gain of electrons
• oxidising agent

Question 24

table of standard reduction potentials

Answer 24

-hardest (non-spontaneous) to reduce to easiest to reduce
- more reactive –> easier to be oxidised –> easier to lose electrons
- the least reactive –> easier to reduce –> don’t tend to lose electrons

Question 25

galvanic cells

Answer 25

- spontaneous redox reaction to create an electrical current - transfer from anode to cathode - converts chemical energy to electrical energy - two half cells that are the site for oxidation and reduction contains: - electrode (anode, cathode) - electrolyte (anolyte, catholyte) - salt bridge - electrical leads - voltmeter

Question 26

electrode

Answer 26

- site where oxidation and reduction occurs - made from metal --> electrically conductive - anode: oxidation half cell - cathode: reduction half cell

Question 27

electrolytes

Answer 27

- facilitate electrical conductivity --> ions as it is aqueous that conducts ions - anolyte: oxidation half cell - catholyte: reduction half cell

Question 28

salt bridge

Answer 28

- closes the electrical circuit - maintains electrical neutrality

Question 29

three types of galvanic cells

Answer 29

- two reacting electrodes - non-reacting electrode - gaseous redox reaction (one s a gaseous reagent at least)

Question 30

inert electrodes

Answer 30

- graphite - lead

Question 31

standard potential of a glavanic cell

Answer 31

amount of electricity that can be generated at a standard state - oxidation (reverse sign) + reduction - must be positive as it is spontaneous

Question 32

how is a reaction caused

Answer 32

successful collision - sufficient kinetic energy - successful orientation

Question 33

collision theory

Answer 33

- all molecules move around and collide independently - chemical reaction only results from a successful collision assumptions: 1. molecules are in a spherical shape 2. molecules travel through the air in a linear fashion 3. collision only occurs between two molecules 4. either a successful or unsuccessful collision

Question 34

rate of reaction

Answer 34

measure of how quickly the reactants are being consumed or products are being formed - change in concentration of products over time rate of reaction = frequency of collisions times success rate of collisions

Question 35

maxwell boltzmann distribution

Answer 35

describes the molecular distribution of kinetic energy in any sample of matter at a particular temperature - y axis: number of particles - x axis: kinetic energy (J)

Question 36

activation energy

Answer 36

minimum energy that a molecule must possess in order for it to undergo a successful collision (chemical reaction) - difference in reactants and peak of curve (energy profile diagrams)

Question 37

surface area (maxwell boltzmann)

Answer 37

- increases particles - increased collisions - increased rate of reaction (success rate does not change) - shifts up

Question 38

concentration (maxwell boltzmann)

Answer 38

- only the concentration of aqueous or gaseous species can be increased - increased number of collisions - increased rate of reaction (success rate does not change) - shifts up

Question 39

temperature (maxwell boltzmann)

Answer 39

- shifts peak to the right (average kinetic area has increased) - area under the curve must be constant (number of particles has not changed --> gets lower) - increases reaction rate and total frequency of collisions

Question 40

catalyst (maxwell boltzmann)

Answer 40

- decreases activation energy - increases rate of reaction - increases success rate of collisions

Question 41

catalyst

Answer 41

non reagent that increases the reaction rate of a substance by providing and alternate pathway that lowers the activation energy

Question 42

energy profile diagrams

Answer 42

show the change in internal energy over the course of a reaction - exo: reactants > products (energy is released) - endo: reactants < products (energy is absorbed) - activation energy --> difference in reaction and peak of curve - only the catalysts changes the energy profile diagram --> decreases the activation energy as it provides an alternate pathway