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Chemistry 5.1.2: How Far? > Rate Equation and Constant > Flashcards

Rate Equation and Constant Flashcards

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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?

A

nothing

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?

A

nothing

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
Q

if pressure increases, explain what happens to the composition of equilibrium

A
  • shifts to side with fewer gas molecules
  • increase in the product/reactant of this side
26
Q

if temperature increases and equilibrium shifts left, explain what has happened to the value of Kc

A
  • decreased
  • backwards = endothermic
  • so forwards = exothermic
  • more reactants are formed
27
Q

disadvantages of high pressure

A
  • can be dangerous
  • expensive
28
Q

advantages of high pressure

A
  • shifts equilibrium to fewest gas molecules
  • if fewer on right, more products form
  • more energy and collisions
29
Q

disadvantages of high temperature in an exothermic reaction

A
  • shifts in endothermic direction
  • so more reactants are formed instead of products
30
Q

advantages of high temperature

A
  • molecules have more kinetic energy
  • more collisions
  • rate increases
31
Q

advantages of using a catalyst

A
  • provides alternate reaction pathway
  • more molecules exceed activation energy
  • reaction can take place at a lower temperature
32
Q

define rate of reaction

A

change in concentration over time

Chemistry 5.1.2: How Far? (3 decks)

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