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Chemistry 5.1.1: How Fast? > exam questions > Flashcards

exam questions Flashcards

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1
Q

explain why an excess of a reactant may be used (2)

A
  • the concentration remains constant
  • it will be zero order
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2
Q

how would you show that a reaction is first order using a graph? (2)

A
  • draw two half lives
  • half life will be constant
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3
Q

how would you determine the initial rate of reaction on a rate time graph? (2)

A
  • draw a tangent at T=0
  • change in y / change in x
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4
Q

how can orders be worked out from a set of results? (3)

A
  • first order = concentration and rate increase proportionally
  • zero order = concentration has no effect on rate
  • second order = concentration changes rate proportionally squared
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5
Q

what order does a negative linear concentration time graph show? (1)

A

zero

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6
Q

what order does a positive linear rate time graph show?

A

first

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7
Q

how is activation energy calculated from a graph? (2)

A
  • change in y / change in x
  • x 8.314
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8
Q

what part of arrhenius is represented by y? (1)

A

lnk

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9
Q

what part of arrhenius is represented by m? (1)

A

-Ea / R
(gradient)

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10
Q

what part of arrhenius is represented by x? (1)

A

1/T

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11
Q

what part of arrhenius is represented by c? (1)

A

lnA
(y intercept)

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12
Q

how is A calculated from an lnk 1/T graph? (2)

A
  • identify where line of best fit crosses y axis
  • inverse log (e power) this value
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13
Q

what are the units for Ea in the arrhenius equation? (1)

A

J mol -1

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14
Q

what experimental methods allows rate of reaction to be measured over time? (2)

A
  • measuring mass loss
  • measuring volume of gas produced
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14
Q

how is J mol -1 converted to kjmol-1? (1)

A

x 1000

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15
Q

what apparatus would allow gas volume to be collected? (1)

A

gas syringe

16
Q

describe a catalyst in a multi step mechanism (2)

A
  • used and reformed
  • only in overall equation, not rate equation
17
Q

state what is meant by rate determining step (1)

A

slowest step in multi step mechanism

18
Q

how would you find k from a rate concentration graph?
(rate equation given) (3)

A
  • rearrange rate equation
  • sub rate and concentration in at the same point
  • units
19
Q

suggest 2 reasons why it is unlikely that a reaction could take place in one step (2)

A
  • rate equation does not match whole equation stoichiometry
  • collision unlikely with more than 2 species

Chemistry 5.1.1: How Fast? (6 decks)

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