Rate Equation and Constant Flashcards

1
Q

what is the rate constant (Kc)?

A

the equilibrium constant

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2
Q

what is the Kc equation?

A

[products] / [reactants]

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3
Q

what do powers represent in the Kc equation?

A

the number of moles in the equation

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4
Q

what are the units?

A

moldm-3 s-1

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5
Q

what is meant a reversible reaction?

A

reaction goes forwards and backwards

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6
Q

describe the forwards reaction

A

initially reactants are used up quickly but rate slows as concentration decreases

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7
Q

describe the backwards reaction

A

initially reactants are reformed slowly but this increases as product concentration increases

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8
Q

what is meant by dynamic equilibrium?

A

rate of forwards reaction = rate of backwards reaction
- concentrations of each substance remains constant

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9
Q

what is a homogenous Kc reaction?

A

all reactants and products are in the same state so are all used in the final expression

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10
Q

what is a heterogenous Kc reaction?

A

reactants and products in different states so solids and liquids not in final expression due to their concentrations remaining constant

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11
Q

state what would happen to the equilibrium composition of a mixture if more reactants are added

A
  • shifts right
  • to reduce amount of reactants
  • and counteract the change
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12
Q

what would happen to the Kc value if more reactants are added?

A

nothing

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13
Q

what would happen to the equilibrium position if the concentration of a catalyst increased?

A
  • position isn’t affected
  • established more quickly
  • because rate of forwards and backwards reactions are equal
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14
Q

what does it tell us if temperature increases and Kc decreases?

A
  • more reactants are reformed
  • reaction has shifted left
  • forwards reaction is exothermic
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15
Q

when does pressure affect Kc?

A

when there are more gas molecules on one side
- if pressure increases, shifts towards fewest gas molecules

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16
Q

describe the effect of temperature on Kc

A
  • increasing temperature shifts equilibrium in the endothermic direction
  • decreasing temperature shifts equilibrium in the exothermic direction
  • if forward reaction is endothermic, Kc increases
  • if forward reaction is exothermic, Kc decreases
17
Q

the student added more reactants to the mixture; what would happen to the equilibrium constant and why?

A
  • shifts right
  • form more products
  • decrease amount of reactants
18
Q

what happens to the value of Kc if reactant concentration increases?

19
Q

what would happen to the equilibrium position if the concentration of the catalyst increases and why?

A
  • nothing
  • equilibrium is established more quickly
  • rate of forwards and backwards reaction increases equally
20
Q

comment on the value of Kc and equilbrium if temperature increases, resulting in more product formation

A
  • reaction shifted right
  • forwards = endothermic
  • Kc increases
21
Q

state 2 features of a system in dynamic equilibrium

A
  • backwards rate of reaction = forwards rate of reaction
  • concentrations remain constant but are constantly interchanging
22
Q

what is the effect of pressure on Kc?

23
Q

if temperature increased and Kc decreased, what has happened to the equilibrium position?

A
  • shift left
  • as backwards = endothermic and forwards = exothermic
  • reforms reactants
24
Q

suggest why methanol is added to petrol

A

adds oxygen

25
if pressure increases, explain what happens to the composition of equilibrium
- shifts to side with fewer gas molecules - increase in the product/reactant of this side
26
if temperature increases and equilibrium shifts left, explain what has happened to the value of Kc
- decreased - backwards = endothermic - so forwards = exothermic - more reactants are formed
27
disadvantages of high pressure
- can be dangerous - expensive
28
advantages of high pressure
- shifts equilibrium to fewest gas molecules - if fewer on right, more products form - more energy and collisions
29
disadvantages of high temperature in an exothermic reaction
- shifts in endothermic direction - so more reactants are formed instead of products
30
advantages of high temperature
- molecules have more kinetic energy - more collisions - rate increases
31
advantages of using a catalyst
- provides alternate reaction pathway - more molecules exceed activation energy - reaction can take place at a lower temperature
32
define rate of reaction
change in concentration over time