unit three: physical chemistry Flashcards
what is the test for lithium
dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.
what is the observation when testing lithium
a bright red flame
what is the test for sodium
dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.
what is the observation when testing sodium
yellow flame
what is the test for potassium
dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.
what is the observation when testing calcium
orange-red flame
what is the test for calcium
dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.
what is the test for copper
dip a nichrome wire in hydrochloric acid to clean it,,. pick up some of the crystals on the wire and hold them on the edge of a blue bunsen flame.
what is the observation when testing copper
green flame
what is the test for aqueous copper
add aqueous sodium hydroxide a drop at a time to form a precipitate.
what is the observation when testing aqueous copper
blue precipitate
what is the test for aqueous iron (II)
add aqueous sodium hydroxide a drop at a time to form a precipitate.
what is the observation when testing aqueous iron (II)
green precipitate
what is the test for aqueous iron (III)
add aqueous sodium hydroxide a drop at a time to form a precipitate.
what is the observation when testing aqueous iron (III)
brown precipitate
how do you test for ammonia
add aqueous sodium hydroxide to the solid or solution under test and warm the mixture
what is the observation when testing for ammonia
a pungent-smelling gas is produced. the gas produced turns damp red litmus paper blue
what is the test for chlorine
to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate solution.
what is the observation when testing for chlorine
white precipitate
what is the observation when testing for bromine
cream precipitate
what is the test for bromine
to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate solution.
what is the test for iodine
to an aquous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate.
what is the observation when testing for iodine
yellow precipitate
what is the test for sulphate
to an aqueous solution of the solid under test, add dilute hydrochloric acid followed by a few drops of barium chloride solution
what is the observation when testing for sulfate
white precipiate
what is the test for carbonate
to either the solid, or an aqueous solution of the solid under test add dilute hydrochloric (or nitric) acid.
what is the observation when testing for carbonate
bubbles of gas. the gas produced turns limewater milky.
Q =
m x c x Δt
ΔH =
Q / n
exothermic
energy is given out
endothermic
energy is taken in
example of an exothermic reaction
the reaction between sulfuric acid and magnesium
example of an endothermic reaction
the reaction between sodium hydrogen carbonate and citric acid
what is specific heat capaacity
the amount of heat needed to raise the temperature of a substance by 1 degree celsius
specific heat capacity of water
4.18 J/g/degree celsius
breaking bonds
needs energy
making bonds
releases energy
what does anhydrous mean
without water
if you heat blue copper sulfate crystals until they turn to a white powder and then and water to it again what happens
it turns blue again and is very warm.
what is the reversible reaction symbol
⇌
if you heat ammonium chloride what happens
the white crystals disappear from the bottom of the tube and reappear further up. it splits it into the colourless gasses ammonia and hydrogen chloride
the stronger the bond
the more energy is required to break it
what are bond energies measured in
kJ/mol
is breaking bonds endo or exothermic
it needs energy, so endothermic
is making bonds endo or exothermic
it releases energy so exothermic
which type of substance are bond energy calculations used for
covalent molecules
if the sign of the overall bond energy calculation is negative what does it mean
heat is given out as the bonds rearrange. the reaction is exothermic
if the sign of the overall bond energy calculation is positive what does it mean
heat has been absorbed as the bonds rearrange, the reaction is endothermic
what is a closed system
no substances are added to the reaction mixture and no substances escape from it. heat may be lost or absorbed.
what is dynamic equilibrium
rate of forward reaction = rate of backward reaction
what is the forward reaction
left to right
what is the backward reaction
right to left
when does the position of equilibrirum lie to one direction
if the reaction is at equilibrium but htere is more of the left substance than the right substance then the position of equilibrium lies to the left, and vice versa
how would you change rate of reaction
change pressure
change temperatyre
add a catalyst (this has no effect on the position of equilibrium)
exothermic changes apart from burning:
the reactions of metals with acids
neutralisation reactions
displacement reactions
what is enthalpy change
the amount of heat energy taken in or given out in a chemical reaction
enthalpy is the difference between
energy of the products and energy of the reactants
does endothermic have a negative or positive enthalpy change
a positive because the reactants are absorbing heat
does exothermic have a negative or positive enthalpy change
negative because the reactants are losing heat
how do you make a substance decompose
heat it constantly
what is specific heat capacity
the amount of heat needed to raise the temperature of 1 gram of substance by 1 degree
is combustion a endothermic or exothermic reaction
exothermic reaction
major errors in evaluation of experimental results for enthalpy changes
large amounts of heat loss
could be incomplete combustion
how can you tell if an alcohol is combusting completely
the flame should be blue and carbon dioxide should be produced instead of carbon
how can you tell if an alochol is combusting incompletely
the flame of the wick is often yellow orange and carbon is produced.
what does (in) excess mean
more than enough of a reactant is present to ensure all of the other reactant(s) react
breaking bonds is
endothermic
making bonds is
exothermic
what are bond energies measured in
kJ/mol
bond energy definition
the amount of energy needed to break 1 mole of covalent bonds in gaseous molecules
what does a sealed container/closed system mean
no substances are added to the reaction mixture and no substances escape from it.
heat can be given off or absorbed.
define dynamic equilibrium
the total amounts or concentrations of the reactants and products are now constant.
give features of dynamic equilibrium (5)
rate of forward reaction = rate of backward reaction
closed system
the concentrations of the reactants and products don’t need to be equal
the concentrations of the reactants and products must remain constant
concentration change in the reaction
the reaction from left to right is the
forward reaction
the reaction from right to left is the
backward reaction
what does the position of eqilibrium mean
a reference to the proportion of the reactants and products in an equilibrium mixture. if the position of a reaction lies towards the right, the equilibrium mixture contains a higher proportion of products than reactants.
what things would you change in an attempt to influence the reaction
change the pressure
change the temperature
add a catalyst
effect of increasing pressure on a reaction in equilibrium
the position of equilibrium shifts to the side which has fewer gas molecules
effect of decreasing pressure on a reaction in equilibrium
the position of equilibrium shifts to the side which has fewer gas molecules.
effect of increasing temperature on a reaction in equilibrium
the position of equilibrium shifts in the endothermic direction
effect of decreasing temperature on a reaction in equilibrium
the position of equilibrium shifts in the exothermic reaction
how would you make a reaction of hydrated to anhydrous substance happen
heat it
how would you make a reaction of anhydrous to hydrated substance happen
add water
specific heat capacity of water
4.18
moles =
mass / Mr
moles =
solution volume x concentration
symbol for enthalpy change
ΔH
symbol for energy change
Q
moles =
gas volume / 24
sources of error in combustion calorimetry
heat loss to surroundings
heat loss to apparatus
incomplete combustion (CO or C formed instead of CO2
evaporation of fuel (hot fuel escapes after burner extinguished)
energy change for reaction (energetics) =
energy change in breaking bonds - energy change in making bonds
break - make
unit for specific heat capacity?
J/g°C
or
J/kg°C
what type of reaction is thermal decompistion
endothermic
why do reactions either give out or absorb heat
during chemical reactions bonds in the reactants have to be broken and new ones have to be
breaking bonds…
needs energy
making bonds…
releases energy
what is the rate of a reaction
the speed at which the amount of reactants decreases or the amount of products increases
what is rate measured as
a change in the concentration (or amount) of reactants or products per unit time
rate of reaction =
time
the steeper the slope/line,
the faster the reaction
how can you measure how fast the reaction is going at any point
by finding the slope (gradient) of the line at that point)
how do you explain the shape of the curve on a graph
using collision theory
what is activation energy
the particles have to collide with a minimum amount of energy in order for a reaction to actually happen.
what are successful collisions
the collisions with energy greater than or equal to the activation energy
when the graph’s line is flat or horizontal what does it mean
all of one of the reactants have been used up, so the reaction has stopped
why are reactions faster if the solids present are in lots of pieces
the surface area in contact with the gas or liquid is larger and there are more particles if the solid exposed on the surface. only the particles on the surface are available for collisions. the frequency of successful collisions increases as the surface area of the solid increases.
what is a catalytic converter
it uses expensive metals such as platinum coated onto a honeycomb structure in a very thin layer for maximum possible surface area.
what happens if you reduce the concentration of an acid or alkali in a reaction
the reaction slows
why does the reaction slow down when concentration is reduced
the number of acid particles decrease, are therefore less close together and collide less frequently. there are fewer succcessful collisions every second.
why does increasing temperature speed up the rate of reaction
the particles are moving faster and so collide more frequently. that will make the reaction go faster, but it only accounts for a small part of the increase in rate. it also increases the number of particles with energy greater or equal to the activation energy, so it will be more likely that two particles which have sufficient energy will collide and react with each other, so frequency of successful collisions increases.
why does increasing pressure increase rate of reaction
it forces particles closer together so that they collide more frequently.
why does decreasing pressure decrease rate of reaction
it allows particles to spread out so frequency of successful collisions decreases.
what are catalysts
substances that speed up chemical reactions but arent used up in the process. they remain chemically unchanged at the end of the reaction.
do different reactions use different catalysts
yes
what are enzymes
biological catalysts
how can you show that a substance is chemically unchanged by the end of a reaction
weigh it before and after you add it to the catalyst solution. the mass should not have changed.
how does a catalyst work
it provides an alternative route for the reaction involving a lower activation energy.
