module 3 Flashcards
what are the two types of changes
- physical: does not result in the formation of new substances
- chemical: involves the formation of new substances
indicators of a physical reaction
- change in state
- change in size/shape
eg. synthesis and decomposition
indicators of a chemical change
- production of bubbles that indicates the a gas has been formed
- production of odour
- change in temperature
- formation of a precipitate
what are the six types of reactions
- synthesis
- decomposition
- combustion (+incomplete)
- precipitation
- acid + base
- acid + carbonate
synthesis reaction
reaction between two or more substances to form a new substance
- two metals –> ionic
- non-metal + metal –> covalent
decomposition
where one reactant is broken into two or more constituent substances and requires the input of energy to break bonds
- thermal decomposition
- electrolysis
- photolysis
combustion
- 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)
precipitation
mixing two solutions together resulting in the formation of a insoluble solid –> precipitate
- predicted using solubility rules
- nagsag
- care bear stroller
acid base (neutralisation)
- acid + base –> salt + water
- exothermic
acid carbonate
- acid + carbonate –> salt + water + carbon dioxide
process of cycads
- 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
metal and steam
hydrogen gas and metal oxide
metal and water
metal hydroxide and hydrogen gas
metal and oxygen
metal oxide
metal and dilute acid
salt and hydrogen gas
displacement reactions
the more reactive metal displaces the less reactive metal ions from the solution
atomic radius
- increases across the group and decreases down the period
- larger atomic radius –> the zeff is lower –> easier to remove electrons –> more reactive
ionisation energy
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
electronegativity
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
oxidation number/state
hypothetical charge of an atom if all bonding was ionic –> degree of oxidation
- neutral atoms/one element = 0
- overall oxidation state of a compound = 0
- ions or polyatomic ions = overall charge
- fluorine = -1
- hydrogen = +1 (covalent) [-1 in hydrides]
- oxygen = -2 in compounds (-1 peroxide)
redox reaction
- oxidation and reduction occur
- oxidation of one or more species has changed
oxidation
- increase in oxidation state
- loss of electrons
- reducing agent
reduction
- decrease in oxidation state
- gain of electrons
- oxidising agent
table of standard reduction potentials
-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
galvanic cells
- 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
electrode
- site where oxidation and reduction occurs
- made from metal –> electrically conductive
- anode: oxidation half cell
- cathode: reduction half cell
electrolytes
- facilitate electrical conductivity –> ions as it is aqueous that conducts ions
- anolyte: oxidation half cell
- catholyte: reduction half cell
salt bridge
- closes the electrical circuit
- maintains electrical neutrality
three types of galvanic cells
- two reacting electrodes
- non-reacting electrode
- gaseous redox reaction (one s a gaseous reagent at least)
inert electrodes
- graphite
- lead
standard potential of a glavanic cell
amount of electricity that can be generated at a standard state
- oxidation (reverse sign) + reduction
- must be positive as it is spontaneous
how is a reaction caused
successful collision
- sufficient kinetic energy
- successful orientation
collision theory
- 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
rate of reaction
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
maxwell boltzmann distribution
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)
activation energy
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)
surface area (maxwell boltzmann)
- increases particles
- increased collisions
- increased rate of reaction (success rate does not change)
- shifts up
concentration (maxwell boltzmann)
- 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
temperature (maxwell boltzmann)
- 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
catalyst (maxwell boltzmann)
- decreases activation energy
- increases rate of reaction
- increases success rate of collisions
catalyst
non reagent that increases the reaction rate of a substance by providing and alternate pathway that lowers the activation energy
energy profile diagrams
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
