6-rate And Extent Of Chemical Change Flashcards
Rate of reaction
Measure of how quickly a reactant is used up or produced formed
Mean rate of reaction
Quantity of reactant used OR quantity of product formed/ time taken
1/time taken (used for when one end point is taken)
Rate of reaction on graphs
The steeper the lline, greater rate of reaction
-gradient = rate of reaction
For calculating mean rate over a period of time
- use graph to find values
- sub values into equation
For calculating rate at a certain point in time
- draw tangent, find gradient of tangent using
- gradient = rise/run
How to see if a reaction is faster
Line becomes horizontal sooner
Measuring rates when a gas is produced
- mass balance- to measure mass lost
- use gas syringe which measures amount of gas produced
- use test tube in water trough, tube moves up and gas amount measured in measuring cylinder
Measuring rate when solid (precipitate produced
Place concical flask on cross
Time amount until you can. No longer see the cross
Hoe does temp increase affect rate of reaction
- reactant particles have more kinetic energy- move faster
- higher chance of collisions, higher frequency of successful collisions between reactant particles
- rate of reaction increases
How does pressure/conc of reacting solution afffect rate of reaction
- reactant particles become more crowded
- presure-gas
- conc-liquids and solids
How does SA:V affect rate of reaction
More reactant particles exposed at surface
How do catalysts affect rates of reaction
-provide alternative reaction pathway which has a lower activtion enery
-doesnt alter products of reaction
-overall energy change the same
0not chemically changed or used up
For a reaction to take place
- reactant particles must collide with each other
- particlles must have enough enrgy to react
Greater frequency of successful collisions
Greater rate of reaction
Equilibrium
Rate of forward reaction = rate of reverse reaction
-when a reversible reaction occurs in a closed system
Reaching equilibrium
-as conc of product builds up, the rate at which they reform increases
rate of forward reaction decreases
-conc of reactant is decrreased from origional maximum value
-eventually both forward and reverse reactions happen at same rate but in opposite direction
-no chang in amount of products and reactants
-has reached equilibum
-as forward and reverse reactions are continously taking place
-dynamic equilibrium
Effect of changing conditions on equililbrium
If a change is made- the system responds to counteract the change
Effect of changing conc
If increased- more products formed until equilibrium reached
If decreased- more reactants will react until equilibrium is reached
Effect of temp change on equilibrium-increased
-relative amount of product at equilibrium increases for an endothermic reaction
Effect of temp change on equilibrium-decreased
- endo-relative amount of products at equilibrium will decrease
- exo-increases
Effectof pressyre change for gaseous reactants
Increase-equilibrium position shifts towards side with smaller nmber of molecues as shown in symbol equation
Decrease-shift towards side w/ larger number of molecules
Effect of pressure change when number of molecules on each side are equal
-changing pressure has no effect but will speed up forward and reverse reaction by same amount
NPK fertilisers
-contain compounds of nitrogen, phosphorous and potassium
in order to improve agricultural productivity
-plants need nitrogen to produce proteins
-formulations of varois salts containing appropriate % of elements
Ammonia
Manufacture ammonium salts and nitric acid
Potassium chloride/sulfate rock
- obtained from mining
- phosphate rock not used directlyas fertilisers
Phosphate rock
- not used directly to fertilise
- treated w/ nitric acid/sulfuric acid to produce soluble salt to be used as fertilisers
Reversible reactions
- when products of the reaction can react to produce the origional reactants
- direction can be changed by changing conditions eg. Heat, cool
- if endo in one direction, exo in other
- same amount of energy is transferred either way
Haber process
- used to manufacture ammonia
- used to produce nitrogen based fertilisers
- raw materials are nitrogen and hydrogen
- gases passed over iron catalyst at 450C
- pressure of 200 atm
Nitrogen + hydrogen ammonia
Reaction is reversible so some ammonia breaks back down
-on cooling ammonia liquefies
-remaining H2 and N2 recycled
Nitrogen source for haber process
- free- extracted from air but energy is used seperating nitrogen from air
- fractional distillation of liquid air (-200C)
- liquifying requires enegry as needs to be at high pressure
Hydrogen source for Haber process
- made by reacting methane gas w/ steam at v. High yemp
- methand + steam = hydrogen + carbon monoxide
- water cheap, cost involved in heating reactant mixture
- main cost- methane gas, bought from gas industry eg. Fossil fuel natural gas
