C13-15 GROUPS RATES, HEAT CHANGES Flashcards
alkali metals
the name of the metals in group 1 - lithium , sodium , potassium and so on
group 1 symbols
li - lithium
Na - sodium
K - potassium
reactions of alkali metals with water
metal + water - metal hydroxide + hydrogen
lithium and water
lithium floats and bubble vigorously
sodium and water
sodium melts into a ball and moves around the surface bubbling vigorously
potassium and water
potassium melts into a ball , catches fire and moves around the surface bubbling vigorously
group 1 reactivity
reactivity increases as you move down the group
explaining group 1 activity
when metals react they lose their outer electrons. further down the group there are more shells of electrons so the outer electrons are less attracted to the nucleus and easier to move
halogens
the names given to the non-metals in group 7- fluorine, chlorine , bromine and iodine
chlorine
CL2 a pale green gas
bromine
BR2 a red brown liquid
iodine
l2 a shiny purple black solid
reaction of halogens with metals
halogen + metal - metal halide
reactions of halogens with hydrogen
halogen + hydrogen - hydrogen halide
hydrogen halides
hydrogen halides dissolve in water to form acids, for example hydrogen chloride makes hydrochloric acid
chlorine test
chlorine gas turns damp blue litmus red then quickly bleaches it white
group 7 activity
reactivity increases as you go up the group
explaining group 7 reactivity
when non-metals react they complete their outer shells. further up the group the elements have fewer shells so the nucleus attracts electrons more strongly
displacement reactions
reactions in which a more reactive metal displaces a less reactive metal from a salt eg.
copper sulfate + zinc - zinc sulfate + copper
does not work backwards as copper is less reactive than zinc
displacement reactions of halogens
a more reactive halogen displaces a less reactive halide ion by taking its electrons
redox reactions of halogens
the more reactive halogen oxides the less reactive halide by taking its electrons. the more reactive halogen is reduced
noble gases
the name given to the non-metals in group 0 - helium , neon, argon, krypton and xenon
melting point of noble gases
they are all gases at room temperature but the melting and boiling point increase down the group
reactivity of group 0
the noble gases do not (easily) do any reactions - they are inert
explaining reactivity of group 0
when elements react they try to complete their outer shells because group 0 outer shell are already complete , they do not react
uses of noble gases
hellium is used in airships because it is inhert and has low density
argon is used in fire extinguishers because it is inhert and denser than air
mean is used in lighting because it glows red when electricity is passed through it
rate of reaction
the rate at which reactants are used up or products are made
reactants vs time graphs
starts high and curves downward , decreasing rapidly at first and then more gently. steeper line = faster rate
products vs time graph
starts low and curves upwards, increasing rapidly at first and then more gently. steeper line = faster rate
measuring rates - reactions that produce gas
collect gas in a gas syringe and measurlthe volume every 30 seconds
collect gas over water and measure volume every 30 secs
do not reaction on a balance and record the change in mass every 30 secs
measuring rates - reactions that go cloudy
do the reaction in a beaker placed on piece of paper with a cross marked on it looking down through the beaker , time how it takes for the crops to disappear
collision theory
states for two particles to react they must:
collide with each other
collide with enough energy to react
activation energy
the minimum energy that two particles must have when they collide in order to react
effect of concentration on rate
increasing the concentration increase the rate because there are more particles so there are more collisions and more reactions
effects of surface area on rate
increasing the surface area (by decreasing particle sizes) in creases the rate by exposing more particles to collisions leading to more collisions and more reactions
effect of pressure on rate
increasing the pressure increases the rate because particles are pushed closer together sp they collide more often
effect of temperature rate
increasing the temperature increases the rate because particles move faster so they collide more , and collide with more energy to a greater proportion to collisions lead to reactions
catalyst
a substance that speeds up a chemical reaction without being used up
effects of catalysts on rate
catalysts increase the rate of reaction by reducing the activation energy so that a greater proportion of collisions lead to reactions
reaction profile
a graph that shows the changes in energy during a reaction starts with large ‘hump’ that represents the activation energy
effects of catalysts on reaction profiles
the hump representing the activation energy is smaller
enzyme
a protein that works as a catalyst to speed up the reactions in our cells
enzymes in alcohol production
alcoholic drinks are produced using enzymes found in yeast which catalyst a reaction that urns glucose into ethanol
exothermic reactions
a reaction that transfers energy to the surroundings( gets hotter)
exothermic reaction examples
neutralisation displacement combustion some precipitation respiration
endothermic reaction
a reaction that absorbs energy from the surroundings
endothermic reaction examples
dissolving (most) salts
some precipitation
photosynthesis
exothermic reaction profile
the reactants have more energy than the products so their line on the graph is higher
endothermic reaction profile
the reactants have less energy than the products so their line on the graph is lower
measuring energy changes
sit a polystyrene beder inside a glass beaker (insulation)
measure the starting temperature of the reactants
mix the reactants in the polystyrene beaker
cover the lid fitted with a thermometer
monitor and record the lowest temperature q
chemical bonds in reaction.
during chemical reactions , old chemical bonds are broken and new ones are formed
breaking bonds
breaking bonds absorbs energy breaking stronger bonds absorbed more energy
making bonds
making bonds releases energy making stronger bonds releases more energy
energy changes and bond information
the energy change in a reaction is the difference between the energy required to break the old bonds and the energy released by making the ew ones
exothermic reactions and bonds
exothermic reactions break weaker bonds and make stronger ones
endothermic reactions and bonds
endothermic reactions break stronger bonds and make weaker ones
bond strengths
the energy required to break one mole of a particular covalent bond in kj/mol
calculating energy changes from bond strength
add up the total strength of old bonds broken and subtract the total strength of new bonds made. a negative answer is a exothermic
