Rate And Extent Of Chemical Changes Flashcards
How can mean rate of reaction be calcukated
Quantity of reactant used/formed
————————————————— = mean rate of reaction
Time taken
What do flat lines and steepnes of line show on graphs for rate of reaction
Flats lines: finished reaction
Steep lines: faster rate of reaction and more product
What does rate of reaction depend on
1)temperature
2) surface area- of solids
3) concentration of solution or pressure of gas
4) Presence of a catalyst
How does implementing factors such as increased temp, surface area, concentration and presence of a catalyst increase rate of reaction
Temp increase increases particles kinetic energy of particles= more collisions = more enegy of reaction
Increased surface area= more area for collisions to occur= greater rate of reaction
Solution more concentrated= more particles in same volume= collisions between reactant particles more frequent increasing rate of reaction
Catalysts speed rate of reaction without being used up. It decreases activation energy by providing an alternative reaction pathway =less collisions needed for reaction= increasing rate or reactions
How to measure rate of reaction experiments
1) Precipitation and colour change
2) Change in mass
3) volume of gas
1) Visual change in a reaction recorded if initial solution is transparent and the product is a precipitate
A mark can be observed and viewed until it disappears
Reactions viewed until it loses colour or gains colour
If you use this method you can’t plot a reaction graph
2) Change in mass can be recorded using a balance
As gas is released the balance reading decreases
The quicker it decreases the faster rate of reaction
Take measurements at intervals. This method can be used for a reaction graph although a disadvantage is that it releases gas into the room
3) A gas syringe can be used to measure volume of gas produced
More gas given off = faster rate of reaction
Measurements can be taken at regular intervals and can be plotted for a reaction graph a disadvanatage can be the plunger blowing out the end of the syringe if the reaction is too vigorous
Required practical: two rate experiments
1-5 magnesium and Hcl produces hydrogen
onwards sodium thiosulfate and hcl produces cloudy precipitate
1) Add a set volume of dilute hcl to a conical flask and carefully place on a balance
2) Add magnesium ribbon to the acid and plug the flask with a cork
3) start a stopwatch and record the mass balance at regular intervals
4) plot results and work out mass lost
5) Repeat with more concentrated acid solution
1) add a set volume of dilute sodium thiosulfate to a conical flask
2) mark a piece of paper and place the flask ontop and pour dilute hcl inside
3) watch the black cross fully disappear and record the time it takes
4) Experiment can be done using different concentrations. Higher concentration = quicker rate of reaction
5) draw a graph of concentration against 1/time for approximate rate
How to calxukate mean rate of reaction from a graph
Change in y value divided by time taken
What happens during a reversible reaction
As reactants reacts the concentration fall- so forward reactions will slow down but as products are made their concentration rises, backwards reaction speeds up
The forward reaction will eventually be in equillibrium with the backwards rate - concentration of both reactants and products are the same.
Equillibrium only happens in a closed system
What factors effect equillibrium
What does the reactants or products being in equillibrium mean
Temperature,pressure,concentration
Reactants in equillibrium = reactants concentration greater then products
Products in equillibrium = products concentration greater then reactants
Explain a reverisble reactions with endo/exo thermic processes
Thermal decomposition of hydrated copper sulafte.
_______>
Hydrated copper sulfate <——– anhydrous copper sulfate + water
Blue hydrated copper sulfate crystals heated, water dries off and leaves a white anhydrous copper sulfate powder (endothermic).
Couple drops of water added to the white powder and the blue crystals form (exothermic)
What is le chateliers principle
Le chateliers principle= if conditions change in a reversible reaction at equillibrium, the system will counteract the change
How can temp change, pressure or concentration effect equillibrium
1) temp decrease = equillibrium shifts to the exothermic reaction to produce more heat for a reaction. More products formed from exothermic
If you raise the temp= equillibrium shifts to endothermic direction to try and decrease it. More products gained from endothermic reaction and fewer from the exothermic reaction
2) Increased pressure= equillibrium reduces it- shifts direction whhere there are fewer moledules of gas
Decreased pressure= equillibrium increases - shifts direction where there are more molecules of gas
3) Increased concentration of reactants =system decreases it by making more products
Decreases concentration of products = system reduces the reactants reactants
