6-rate And Extent Of Chemical Change

Question 1

Rate of reaction

Answer 1

Measure of how quickly a reactant is used up or produced formed

Question 2

Mean rate of reaction

Answer 2

Quantity of reactant used OR quantity of product formed/ time taken

1/time taken (used for when one end point is taken)

Question 3

Rate of reaction on graphs

Answer 3

The steeper the lline, greater rate of reaction

-gradient = rate of reaction

Question 4

For calculating mean rate over a period of time

Answer 4

• use graph to find values

- sub values into equation

Question 5

For calculating rate at a certain point in time

Answer 5

• draw tangent, find gradient of tangent using

- gradient = rise/run

Question 6

How to see if a reaction is faster

Answer 6

Line becomes horizontal sooner

Question 7

Measuring rates when a gas is produced

Answer 7

• 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

Question 8

Measuring rate when solid (precipitate produced

Answer 8

Place concical flask on cross

Time amount until you can. No longer see the cross

Question 9

Hoe does temp increase affect rate of reaction

Answer 9

• reactant particles have more kinetic energy- move faster
• higher chance of collisions, higher frequency of successful collisions between reactant particles
• rate of reaction increases

Question 10

How does pressure/conc of reacting solution afffect rate of reaction

Answer 10

• reactant particles become more crowded
• presure-gas
• conc-liquids and solids

Question 11

How does SA:V affect rate of reaction

Answer 11

More reactant particles exposed at surface

Question 12

How do catalysts affect rates of reaction

Answer 12

-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

Question 13

For a reaction to take place

Answer 13

• reactant particles must collide with each other

- particlles must have enough enrgy to react

Question 14

Greater frequency of successful collisions

Answer 14

Greater rate of reaction

Question 15

Equilibrium

Answer 15

Rate of forward reaction = rate of reverse reaction

-when a reversible reaction occurs in a closed system

Question 16

Reaching equilibrium

Answer 16

-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

Question 17

Effect of changing conditions on equililbrium

Answer 17

If a change is made- the system responds to counteract the change

Question 18

Effect of changing conc

Answer 18

If increased- more products formed until equilibrium reached

If decreased- more reactants will react until equilibrium is reached

Question 19

Effect of temp change on equilibrium-increased

Answer 19

-relative amount of product at equilibrium increases for an endothermic reaction

Question 20

Effect of temp change on equilibrium-decreased

Answer 20

• endo-relative amount of products at equilibrium will decrease
• exo-increases

Question 21

Effectof pressyre change for gaseous reactants

Answer 21

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

Question 22

Effect of pressure change when number of molecules on each side are equal

Answer 22

-changing pressure has no effect but will speed up forward and reverse reaction by same amount

Question 23

NPK fertilisers

Answer 23

-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

Question 24

Ammonia

Answer 24

Manufacture ammonium salts and nitric acid

Question 25

Potassium chloride/sulfate rock

Answer 25

• obtained from mining

- phosphate rock not used directlyas fertilisers

Question 26

Phosphate rock

Answer 26

• not used directly to fertilise

- treated w/ nitric acid/sulfuric acid to produce soluble salt to be used as fertilisers

Question 27

Reversible reactions

Answer 27

• 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

Question 28

Haber process

Answer 28

• 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

Question 29

Nitrogen source for haber process

Answer 29

• 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

Question 30

Hydrogen source for Haber process

Answer 30

• 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