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Topic 10: Equilibrium I
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- 1what type of reactions cant be easily reversed?-when enthalpy change is large + negative
reaction goes to completion
- hard to reverse - 2state the characteristics of reversible reactions.-dont go to completion
-contain dectable amounts of reactants mixed with prdocuts
- are shown by double arow instead of 1 arrow - 3what is special about the reaction between hydrogen + iodine to form hydrogen iodide-is reversible
-H2(g) + I2(g)= 2HI(g) - 4what happens in the forward reaction of hydrogen + iodide vapour when in a sealed containerH2(g) + I2(g) = 2HI (g)
as reaction proceeds
-concentration of both H and I decrease
-rate of forward reaction decreases
-conc of HI increases,
-increases the rate of the backward reaction - 5what happens eventually when hydrogen + iodide vapour are in a sealed container? draw a graph to show thisrates of 2 reactions (forward + backward reaction) eventually equalise
= equilbrium established - 6what happens to the position of the equilibrium if you increase the conc of the reactant or decreased the conc of the productequilbrium moves to the right
- 7what happens to the position of the equilibrium if you decrease the conc of the reactant or increase the conc of productequilibrium moves to the left
- 82cro4(2-) + H+ = Cr207 (2-) + H20 (l) 2cro4 = yellow Cr207= orange Describe the observations seens when there is an increase in conc of H+ (aq)- increase in acid= more H+= high conc of reactants
- equilibrium shifts towards products
-more Cr207 is produced
- solution turns orange - 92cro4(2-) + H+ = Cr207 (2-) + H20 (l) 2cro4 = yellow Cr207= orange Describe the observations seens when there is an decrease in conc of H+ (aq)- add alkali = less H+= higher conc of products
- equilibrium shifts in favour of reactants
- more CrO4 produced
-solution turns yellow - 10What is in a dynamic equilibrium ?- the forward + backwards reactions carry on continuously
-rate of forward reaction= rate of backwards reaction
- conc of reactants + products remain constant (doesn't mean equal) - 11what is needed for a dynamic equilibrium to be established?-reaction must be reversible
-reaction mixture must be in a closed container (so no substances enter or leave) - 12Nitrogen reacts with hydrogen to form ammonia -N2(g) + 3h2 (g) = 2NH3 (g) Predict the effect of increasing the pressure of this mixture of gases at equilibrium- position of equilibrium will move to the right because there are fewer moles of gas on the right hand side of the equation
- the equilibrium conc of ammonia will increase - 13what will effect the equilibrium constant for a reaction at equilbrium?-temp change
- 14how does increasing temperature impact a reaction mixture in equilibrium ?-rate of forward + backward reaction both increase
-rate of endothermic reaction increases the most
- moves the position of equilibrium in direction of the endothermic reaction - 15N2 (g) + 3H2 (g) = 2NH3 forward reaction= -92kjmol backward reaction= + 92 kj mol how will temp impact reactions equilibrium?equilibrium will move to the left
-in favour of endothermic reaction (backward reaction) - positive enthalpy change - 16how does addition of a catalyst impact equilibrium of a reaction?-rates of forward + backward reaction both increase
- but by the same ratio
-dosent change position of equilibrium but reduce time needed to reach equilbrium - 17what does Kc stand for?Kc= equilibrium constant
-expressed in terms of concentrations - 18write the equation for Kc from this reaction aA + bB= cC + dD what does this expression define?Kc= [C]^c [D]^d divided by
[A]^a [B]^b
it is conc of products over conc of reactants
defines the equilibrium law - 19give the 2 different systemshomogeneous system
heterogeneous system - 20what is the homogeneous system give an exampleall components are in the same phase/state
e.g. H2(g) + I2 (g) = 2HI (g) - 21what is the heterogeneous system?- 2 or more components are in different phases/states
e.g. CaCO3 (s) = CaO (s) + CO2 (g) - 22Nitrogen reacts with hydrogen to form ammonia: N2 (g) + 3H2 (g) = 2NH3 (g) WRITE AN EXPRESSION FOR THE equilibrium constant , KcKc= [NH3(g)]^2 divided by
[ N2(g)][H2(g) ] ^3 - 23when all components of a reaction appear in the expression for Kc what does it indicate?its a homogeneous system
- 24Calcium carbonate decomposes when heated CaCO3 (s) = CaO(s) + Co2 (g) write an expression for the equilibrium constantKc= [Co2(g)]
- heterogeneous system so at given temp equilibrium conc of solids + temps constant
- only conc of gases or solutions raised to appropriate powers need to be shown - 25what factors affect the equilibrium yield of a product from a reversible reaction- temp of reaction mixture
-conc of reactants
-pressure (if gases are present) - 26are industustrail processes adapted to produce greater product yield?- reaction conditions not necessarily ones that produce greatest yield
- 27what factors impact the rate of reaction?- temp of reaction mixture
-conc of reactants
-particle size of solid reactants
-presence of suitable catalyst - 28an increase in pressure of reacting gases can increase the reaction rate but not if...- uncatalysed rate is very low
-catalyst is present but all of its active sites are occupied - 29what does the Harber process manufacture ? give an equation of this-produces: ammonia
-N2 (g) + 3H2 (g) = 2NH2 (g) - 30a high equilibrium yield is favoured in the Haber process if conditions include..- forward reaction : exothermic
yield favoured by..
- low temp
- high pressure (so fewer moles of gas on the right- product side) - 31what conditions are usually chosen for the Haber process in industry?- 240 atm pressure
- 450 degrees - 32why is 250 atm pressure chosen for the Haber Process?- high enough to get reasonable yield
- not so high expensive to achieve e.g. reinforced equipment ... - 33why is a temp of 450 degrees chosen for the Haber Process in industry- high enough to achieve reasonable rate
-not so high it reduces equilibrium yield (product yield) - 34what catalyst is used in the Haber process? why? how can we reduce the time needed to complete this process?- iron: cheaper than other metals like platinum
- reduce time: reaction not allowed to reach equilIbrium= faster, so yield is 15% - 35Methanol can be manufactured from carbon monoxide and hydrogen CO(g) + 2H2 (g) = CH30H (g) Delta H = -91kjmol-1 Explain why a low temp would favour a high equilibrium yield of methanol?-forward reaction is exothermic
-position of equilbrium moves to the right if the temp is reduced - 36explain why a high pressure would favour a high equilibrium yield of methanol?-there are fewer moles of gas on the right
-position of equilibrium moves to the right if the pressure is increased - 37state 2 reasons why a very high pressure would be uneconomic (2 marks)- STRONG PRESSURE VESSELD WOULD BE NEEDED
-lot of energy would be needed to pressurise it
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- GCSE (Topic 10-14 ) Chemistry Fichas sobre Topic 10: Equilibrium I, creado por Jade B el 20/11/2017.
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- Jade B
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