chem paper 1 questions with complete solutions.

chem paper 1 questions with complete
solutions



Explain why increasing the concentration of H2O2(aq) increases the rate of
c c c c c c c c c c


decomposition. - answer-More particles per (unit) volume.
c c c c c c c


More collisions per second.
c c c




Explain how the catalyst can increase the rate of decomposition of H2O2(aq) - answer-
c c c c c c c c c c c c c


Activation energy is lowered. c c c


More molecules have enough energy to react.
c c c c c c




High pressures and low temperatures would give the maximum equilibrium yield of
c c c c c c c c c c c


cmethanol. - answer-High pressure as fewer moles (of gas) on right-hand side OR
c c c c c c c c c c c c


high pressure as volume of products less than that of reactants
c c c c c c c c c c


low temperature as (forward) reaction is exothermic.
c c c c c c




Explain why the actual conditions used in the chemical industry might be different from
c c c c c c c c c c c c c


those in (a) above. - answer-Too expensive to use a high pressure.
c c c c c c c c c c c c


Too slow to use a low temperature.
c c c c c c




Suggest two ways in which the use of catalysts helps chemical companies to make their
c c c c c c c c c c c c c c


cprocesses more sustainable. - answer-1) Catalyst not used up in reaction
c c c c c c c c c c


reactions take place at lower temperatures c c c c c


with lower energy demand OR lower activation energy OR use
c c c c c c c c c c




2) Less fuel so less carbon dioxide emitted into atmosphere
c c c c c c c c c c




OR so fossil
c c


fuels last longer c c


different reactions can be used c c c c


with better atom economy OR
c c c c c




3) less waste, less hazardous chemicals
c c c c c




State le Chatelier's principle. - answer-when the conditions on a system in equilibrium
c c c c c c c c c c c c


care changed (1)
c c


the equilibrium moves to minimise the effects of the change (1)
c c c c c c c c c c

, Describe, and explain, what would happen to the position of the NO2/N2O4
c c c c c c c c c c c


equilibrium if the following changes are made. c c c c c c


(i) The temperature is increased. * - answer-equilibrium moves towards LHS/ towards
c c c c c c c c c c c


cNO2
(1)
forward reaction is exothermic/ reverse reaction is endothermic (1)
c c c c c c c c




The pressure is increased. - answer-equilibrium moves towards RHS/ towards N2O4
c c c c c c c c c c


(1)
fewer moles on RHS (1)
c c c c




A catalyst is added. - answer-no change in equilibrium position (1)
c c c c c c c c c c


catalyst speeds up forward and reverse reactions by same amount (1)
c c c c c c c c c c




State and explain what effect changing the acid has on the rate of the reaction. - answer-
c c c c c c c c c c c c c c c c


rate is slower because weak acid is partially dissociated
c c c c c c c c


lower concentration of H+, in weak/ higher concentration of H+, in strong/ HCl
c c c c c c c c c c c c




Give two features of a reversible reaction, when a dynamic equilibrium has been set up.
c c c c c c c c c c c c c c


- answer-1) Rate of forward reaction = rate reverse reaction
c c c c c c c c c c


2) concentrations remain constant
c c c


3) closed system needed
c c c




What is meant by a catalyst? - answer-a substance that alters the rate of a reaction
c c c c c c c c c c c c c c c


without being used up /
c c c c c


a substance that lowers the activation energy (for a reaction) by providing an alternative
c c c c c c c c c c c c c


route.
c




What is meant by homogeneous? - answer-catalyst is in the same state as reactants
c c c c c c c c c c c c c




Catalysts do not affect the position of an equilibrium. Explain why not. - answer-they
c c c c c c c c c c c c c


alter the rate of the forward and the reverse reaction by the same amount
c c c c c c c c c c c c c c




Describe and explain why these conditions, pressure and tempaerature are a
c c c c c c c c c c


ccompromise between rate and c c c


equilibrium. - answer-rate 9 c c c


(increased) pressure increases rate because molecules are closer together/ more
c c c c c c c c c


cconcentrated
(increased) temperature increases rate because molecules are moving faster/ have
c c c c c c c c c


cmore energy c


equilibrium
increased pressure pushes equilibrium to RHS because
c c c c c c


fewer (gas) moles/ molecules on RHS
c c c c c


increased temperature pushes equilibrium to LHS
c c c c c


because (forward) reaction is exothermic
c c c c


compromise