P2 6 Rate/extent of chemical change Flashcards

1
Q

describe collision theory

A
  • collision theory: reactant particles must collide with each other (providing particles have sufficient activation energy) to start a reaction
  • a collision that produces a reaction is a successful collision
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2
Q

define activation energy

A
  • activation energy - minimum amount of
    energy needed for a collision to be successful
  • activation energy is diff for different reactions
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3
Q

state factors affecting rate of chemical reactions (5)

A
  • temperature
  • concentration of reactant
  • reacting gas pressure
  • SA:V of solid reactant
  • presence of a catalyst

-> all increase rate when increased

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4
Q

describe how increased temperature increases rate of reaction

A

particles gain more energy so move around quicker and collide more frequently

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5
Q

describe the method for effect of temperature on rate of reaction by measuring change in colour/ turbidity (RP)
using sodium thiosulfate+ hydrochloric acid

A
  • add 50 cm³ of dilute sodium thiosulfate solution to a conical flask
  • place the conical flask on a piece of paper with a black cross drawn on it
  • add 10 cm³ of dilute hydrochloric acid to the conical flask
  • immediately swirl the flask to mix its contents and start a stopwatch
  • look directly down through the reaction mixture, when the cross can no longer be seen record the time on the stopwatch
  • repeat steps with different temperatures of sodium thiosulfate solution
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6
Q

describe how increased concentration of reactant increases rate of reaction

A

more reactant particles in a given volume so more frequent collisions

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7
Q

describe the method for effect of concentration on rate of reaction by measuring volume of gas produced (RP)
using calcium carbonate+ hydrochloric acid

A
  • support a gas syringe with a stand, bung and clamp
  • add 50 cm³ of dilute hydrochloric acid to a conical flask
  • add 0.4 g of calcium carbonate to the flask, immediately connect the gas syringe and start a stopwatch
  • record the volume of gas produced every 10secs until the reaction is complete
  • repeat steps with different concentrations of hydrochloric acid
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8
Q

describe how increased reacting gas pressure increases rate of reaction

A

more reactant particles in a given volume so more frequent collisions

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9
Q

describe how increased SA:V of solid reactant increases rate of reaction

A

-> eg. cutting up the solid into smaller pieces/ into a powder to increase SA
more particles exposed to other reactants so more frequent collisions

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10
Q

describe catalysts and how they increase rate of reaction

A

catalyst - substance which increases rate of reaction without undergoing a permanent change
* they provide a different pathway for the reaction with a lower activation energy
* not included in the equation
* eg. enzymes used in biological systems

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11
Q

describe what a reaction profile looks like for catalysed reactions (vs normal reactions)

A

the curve showing activation energy on the reaction profile will be lower
(as they provide a different pathway for the reaction with a lower activation energy)

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12
Q

state the 2 equations for calculating mean rate of reaction

A

quantity of reactant used / time taken
OR
quantity of product formed / time taken
-> quantity measured in g or cm³ or mol
-> time measured in secs
-> rate measured in g/s or cm³/s (also mol/s)
-> the rate is a mean as the rate varies over time

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13
Q

describe reversible reactions

A

(backwards reaction) ⇌ (forwards reaction)
* direction of reaction is changed by reversing the conditions - if the reactant is heated, the product is cooled
* if the forwards reaction is exothermic (-kJ) , the backwards reaction is endothermic (+kJ)

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14
Q

state Le Chatelier’s principle

A

if a system is at equilibrium and a change is made to its conditions, the system will respond to counteract the change

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15
Q

name the three conditions of dynamic equilibirum

A
  • reaction is reversible
  • reaction is in a closed system
  • forwards reaction rate = backwards reaction rate
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16
Q

describe how the equilibrium shifts when there is an increase in temperature

A

equilibrium shifts to the endothermic side/direction (left or right)

17
Q

describe how the equilibrium shifts when there is an increase in reactant concentration

A

equilibrium shifts to the products

18
Q

describe how the equilibrium shifts when there is a decrease in reactant concentration

A

equilibrium shifts to the reactants

19
Q

describe how the equilibrium shifts when there is an increase in pressure

A

equilibrium shifts to the side with fewer gas molecules

20
Q

describe how the equilibrium shifts when there is a decrease in pressure

A

equilibrium shifts to the side with more gas molecules

21
Q

describe how the equilibrium shifts when there is an added catalyst

A

has no effect on the position - increases rate of reaction on both sides of the equation so is already balanced

(but does allow equilibrium to be reached quicker/ at lower temp)