8/9/2019 kc questions- chemistry

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1. Syngas is a mixture of carbon monoxide and hydrogen gases, used as a feedstock forthe manufacture of methanol.

 A dynamic equilibrium was set up between carbon monoxide, CO, hydrogen, H2, and

methanol, CHOH, in a 2.! dm sealed "essel.

#he equilibrium is shown below.

CO$g% & 2H2$g% CHOH$g%

#he number of moles of each component at equilibrium is shown below

component CO$g% H2$g% CHOH$g%

number of moles atequilibrium '.2! ( )!

 *+.! ( )!

 *2-.2! ( )!

 *-

 

$a% tate two features of a system that is in dynamic equilibrium.

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$b% $i% 1rite an expression for K c for this equilibrium system.

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$ii% Calculate K c for this equilibrium. tate the units.

K c  33333333... units43333..3..

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Brighton Hove and Sussex Sixth Form College 1

8/9/2019 kc questions- chemistry

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$c% #he pressure was increased whilst keeping the temperature constant. #hemixture was left to reach equilibrium.

#he equilibrium position abo"e shifted to the right.

$i% 5xplain why the equilibrium position shifted to the right.

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$ii% 1hat is the effect, if any, on the "alue of K c6

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$d% #he temperature was increased whilst keeping the pressure constant. #hemixture was left to reach equilibrium.

#he "alue of K c for the equilibrium abo"e decreased.

$i% 5xplain what happened to the equilibrium position in the equilibrium.

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$ii% 7educe the sign of the enthalpy change for the forward reaction shown inthe equilibrium abo"e.

5xplain your reasoning.

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Brighton Hove and Sussex Sixth Form College 2  

8/9/2019 kc questions- chemistry

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$e% 8ethanol can be used as an additi"e to petrol.

$i% 1rite an equation for the complete combustion of methanol, CHOH.

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$ii% uggest why methanol is added to petrol.

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2. 1hen heated, phosphorus pentachloride, 9Cl -, dissociates.

9Cl -$g% 9Cl $g% & Cl 2$g%

 A chemist placed a mixture of the three gases into a container. #he initial concentration

of each gas was the same4 !.! mol dm *

. #he container was left until equilibrium had

been reached.

:nder these conditions, K c  !.2+- mol dm *

.

$a% 1rite an expression for K c for this equilibrium.

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Brighton Hove and Sussex Sixth Form College 3

8/9/2019 kc questions- chemistry

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$b% :se the "alue of K c for this equilibrium to deduce whether the concentration of

each gas increases, decreases or stays the same as the mixture approachesequilibrium.

$i% how your answer by placing a tick in the appropriate cells in the tablebelow.

initial concentration

; mol dm *

greater than

!.! mol dm *

less than

!.! mol dm *

equal to

!.! mol dm *

9Cl - !.!

9Cl  !.!

Cl 2 !.!

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$ii% 5xplain your deduction.

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$c% #he chemist compressed the equilibrium mixture at constant temperature andallowed it to reach equilibrium under these new conditions.

$i% 5xplain what happens to the "alue of K c.

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Brighton Hove and Sussex Sixth Form College 4

8/9/2019 kc questions- chemistry

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$ii% 5xplain what happened to the composition of the equilibrium mixture.

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$d% #he chemist heated the equilibrium mixture and the equilibrium mo"ed to the left.

$i% 5xplain what happens to the "alue of K c.

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$ii% 5xplain what additional information this obser"ation re"eals about thereaction.

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Brighton Hove and Sussex Sixth Form College