Science - Chemistry - Rates of reaction - C6 Flashcards
what is the rate of reaction ?
how fast reactants are turned to products
give an example of a slow reaction ?
rusting of iron
give an example of a fast reaction ?
explosion
what things effect rate of reaction ?
- concentration of particles
- catalyst
- surface area
- temperature
how does temperature affect rates of reaction ?
- higher the temp = faster the reaction, as particles have more energy so move faster so there are more collisions
how does surface area affect rates of reaction ?
bigger surface area, faster reaction, larger surface area to volume ratio gives more area for the reaction to happen
how does increased concentration affect rate of reaction ?
it speeds up reaction, as more particles = more collisions so the reaction happens quicker
how do catalyst speed up reactions ?
they decrease the activation energy by providing a faster reaction pathway
what are catalysts ?
a substance which can speed up a reaction without ever being used up in a reaction
what is the collision theory ?
- that the more collisions of reacting particles, the more collisions, the faster the reaction
- energy transferred during collisions increases the rate or reaction by increasing the number of collisions
how does energy increase the rate of reaction ?
more energy speeds up movement of particles which increases collisions
what is activation energy ?
the minimum amount of energy needed to start a reaction
how is the rate of reaction proportional to successful collisions ?
if the rate of reaction is doubled, the number of collisions will double
what is the rate of reaction proportional to ?
successful collisions
give an example of a biological catalyst ?
enzymes
how are enzymes biological catalysts ?
they can catalyse a reaction for specific molecules
how do you calculate the rate of reaction ?
quantity of reactants used or products formed / time
what could rate of reaction be measured in ?
cm3/s
g/s
moles
how can you measure the formation of a product through recording the visual change of a reaction ?
if the initial solution is transparent record the time it takes to become cloudy -
observe a mark through the solution and time how long it takes to disappear
*if reactants are coloured and products are colourless or swapped
how can you measure the formation of a product through speed of reaction when the product is a gas ?
using a mass balance add the eactants to a conical flask and put cotton wool over the neck to stop acid from spitting out and time how long it takes for the gas to be released by watching the mass disappear
what is the advantage of measuring the formation of a product through speed of a reaction when the product is a gas ?
it is accurate
what is the disadvantage of measuring the formation of a product through speed of a reaction when the product is a gas ?
dangerous gases are released into the room
how can you measure the formation of a product through a gas syringe when the gas is a product ?
use a gas syringe to measure the volume of gas given off, the more gas given off the faster the reaction - plot a graph to find the rate of reaction
what is the advantage of measuring the formation of a product through a gas syringe when the gas is a product ?
dangerous gas doesn’t escape
on the graph if the gradient is steeper what is the rate of reaction ?
greater
why is a rate of reaction graph curved ?
reactants start quickly then slow down
why does the reaction start quickly then slow down ?
there’s lots of reactant at the beginning so there is more collisions the reaction slows down because the reactant gets used up
how do you work out the mean rate of reaction from graphs ?
change in y / change in x
how do you work out the rate of reaction from a particular point in the graph ?
draw a tangent then work out the gradient
when we react magnesium and hydrochloric acid, what are we investigating ?
the effect of having an increased reactant concentration on the rate of reaction
what is the equation of magnesium and hydrochloric acid ?
2HCL+Mg - MgCl2 + H2
how do you follow the rate of reaction during the magnesium and HCL experiment ?
reaction gives of hydrogen gas so measure the amount of hydrogen gas produced using a gas syringe
describe step by step the experiment using HCL and magnesium
- measure 50cm3 of dilute HCL to a conical flask
- Add magnesium ribbon and attach an empty gas syringe
- start stopwatch
- take readings of volumes regularly until volume doesn’t change
- table results and draw a graph with time on X and volume on Y
- repeat with a higher concentration in the acid solutions
what does sodium thiosulfate and HCL produce ?
they are both clear substances and reacts to form yellow precipitate
what is the equation when reacting sodium thiosulfate and HCL ?
2HCL + Na2S2O - NaCl + SO + S + H2O
when reacting sodium thiosulfate and HCL what are we investigating ?
looking through the solution at the black cross and measuring how long it takes for the black cross to disappear
describe step by step the experiment mixing HCL and sodium thiosulfate
- add 50cm3 of sodium thiosulfate to a conical flask
- place flask on paper with black cross underneath and add 10cm3 of dilute HCL, swirl briefly and start stopwatch
- watch black cross disappear and record results in a graph
- repeat again for more precise results
- repeat reaction again with a different concentration of either the reactants OR products
what is a reversible reaction ?
the products react to produce the reactants
how is a reversible reaction shown ?
double arrows
what happens if a reversible reaction is in a closed system ?
it reaches equilibrium
what is equilibrium in a reversible reaction ?
the amounts of products and reactants reach a balance and the concentration stops changing
what is a closed systems ?
where no reactants or products can escape the reaction
in a closed system reactants react in this reversible reaction and concentration drops, so the reaction slows down as more products are made. What happens to the rate of reaction in products and how is equilibrium achieved ?
products are made so concentration of product particles increase which speeds up the rate of reaction after a while the reversible reaction reaches an equilibrium as both reactions are happening with no effect
what happens if the equilibrium lies to the right ?
the concentration of products is greater than the concentration of reactants
what happens if the equilibrium lies to the left ?
concentration of reactants is greater than the concentration of products
In reversible reactions and 1 side of the reaction is exothermic, what is the other side ?
endothermic and equal to the energy released as energy absorbed = energy released
what is Le Chateliers principle ?
if you change conditions of a reversible reaction at an equilibrium the system will try to counteract the change so the effect of any changes can be predicted
by using Le Chateliers principle how can you end up with more product than you want ?
by altering the pressure/temperature/concentration you are altering the yield
by using le chateliers principle how can you use temperature ?
if you increase the temperature the yield of the endothermic reaction with increase and the yield of exothermic reactions will decrease and vice versa
by using le chateliers principke how can you use pressure for gases ?
raising the pressure favours the reaction which produces less volume
lowering the pressure favours the reaction which produces more volume
if you increase the concentration of the reactant in a closed reversible reaction at equilibrium what will happen ?
the system tries to decrease it by making products and vice versa
what does greater volume mean ?
there are more gas molecules on that side of the reaction
