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IGCSE Chemistry > Collision Theory - 4th > Flashcards

Collision Theory - 4th Flashcards

1
Q

when can a chemical reaction only happen?

A
  • if the reactant particles collide with enough energy
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2
Q

what is activation energy?

A
  • the amount of energy the particles need to react is called activation energy
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3
Q

what will happen to particles which collide with less energy than the activation energy?

A
  • will just rebound and remain unchanged
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4
Q

what does the overall rate of reaction involving millions of particles depend on?

A
  • collision frequency
  • percentage success
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5
Q

what is collision frequency?

A
  • how often do the particles collide with each other
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6
Q

what is percentage success?

A
  • what percentage of the collisions have enough energy?
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6
Q

what are four common factors which affect rate of reaction?

A
  • surface area
  • concentration
  • temperature
  • catalysts
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6
Q

why does a higher solid surface area increase the rate of reaction?

A
  • more of the solid is exposed to the other particles
  • so the collision frequency is higher
  • so there are more successful collision per unit time
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6
Q

why does a higher temperature a increase the rate of reaction?

A
  • the particles have more kinetic energy
  • so the percentage of collisions with enough energy is higher
  • so there are more successful collisions per unit time
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7
Q

why does a higher solution concentration/gas pressure increase the rate of reaction?

A
  • there are more particles per unit volume
  • so the collision frequency is higher
  • so there are more successful collisions per unit time
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7
Q

why does a catalyst increase the rate of reaction?

A
  • they provide an alternative route with a lower activation energy
  • so the percentage of collisions with enough energy is higher
  • so there are more successful collisions per unit time
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8
Q

how can you increase the concentration of a solution/gases?

A
  • by dissolving more solute particles
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9
Q

how can you increase the pressure of a solution/gases?

A
  • by making the reaction vessel smaller
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10
Q

how can the effect of concentration on rate be demonstrated?

A
  • by reacting sodium thiosulphate solution with hydrochloric acid to make sodium chloride, sulphur solid , sulphur dioxide and water
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11
Q

what is the chemical equation for the disappearing cross experiment?

A
  • Na2S2O3 (aq) + 2HCl (aq) -> 2NaCl (aq) + S (s) + SO2 (g) + H20
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12
Q

describe the observations of the disappearing cross experiment?

A
  • in this reaction, a solid (sulphur) is slowly produced
  • after a while, you cannot see through the mixture any longer
  • this is measured by observing a black cross under the mixture
13
Q

what are the variables for the disappearing cross experiment?

A
  • input : the concentration of the Na2S2O3 (aq)
  • output : the time taken for the cross to disappear
  • control : total volume of solution, concentration of HCl (aq), temperature
14
Q

how is rate calculated?

A
  • rate (s^-1) = 1/time taken (s)
15
Q

what is the relationship between rate and concentration?

A
  • they are proportional
16
Q

how is surface area increased?

A
  • by cutting or grinding up the solid
17
Q

how is the effect of surface area on rate demonstrated?

A
  • by reacting calcium carbonate marble chips with hydrochloric acid to form calcium chloride, water and carbon dioxide gas
18
Q

what is the chemical equation for the marble chip experiment?

A
  • CaCO3 (s) + 2HCl (aq) -> CaCl2 (aq) + H2O (l) + CO2 (g)
19
Q

what are the variables in the marble chip experiment?

A
  • input : the sizes of the CaCO3 (s) chips
  • output: the volume of CO2 (g)
  • control: the mass of CaCO3(s), the volume and concentration of HCl (aq), temperature
20
Q

how is the volume of carbon dioxide measured in the marble chip experiment?

A
  • using a gas syringe or inverted measuring cylinder in water
21
Q

what are the results of the marble chip experiment on a graph of volume of CO2 against time?

A
  • a higher SA has a steeper start than the one with a lower SA because the rate has increased, so the volume of CO2 is increasing faster
  • it has the same final volume of CO2- this is because the total amount of reactants hasn’t changed, so eventually the reaction produces the same amount of CO2
22
Q

how can temperature be increased?

A
  • by heating
23
Q

how can the effect of temperature on rate be demonstrated?

A
  • by reacting magnesium with hydrochloric acid to produce magnesium chloride and hydrogen gas
24
Q

what is the chemical equation for the magnesium and acid experiment?

A
  • Mg (s) + 2HCl (aq) -> MgCl2(aq) + H2
25
Q

describe what happens in the magnesium and acid reaction?

A
  • the magnesium disappears
26
Q

what are the variables in the magnesium and acid experiment?

A
  • input: the temperature of the HCl (aq)
  • output: the time taken for Mg (s) to disappear
  • control: mass and SA of Mg (s) and the volume and concentration of HCl (aq)
27
Q

what are the results of the magnesium and acid experiment on a graph of rate against temperature?

A
  • rate isn’t proportional to temperature so it isn’t a straight line
  • it doesn’t go through the origin because the rate isn’t zero at 0 degrees
28
Q

what are catalysts?

A
  • are substances (usually solids) which increase rate and remain chemically unchanged
29
Q

how can the effect of a catalyst on rate be demonstrated?

A
  • using the decomposition of hydrogen peroxide
  • 2H2O2 (aq) -> 2H2O (l) + O2 (g)
30
Q

describe the results of the hydrogen peroxide experiment?

A
  • very very slow reaction, usually taking days to finish
  • it is catalysed by manganese (IV) oxide (MnO2), which is a black solid
  • this causes it to place much faster, taking only a few seconds to finish
31
Q

what are the variables of the hydrogen peroxide experiment?

A
  • input: which catalyst is being used
  • output: volume of O2 (g)
  • control: volume and concentration of H2O2 (aq), temperature, mass and surface area of catalyst
32
Q

what are the results of the hydrogen peroxide experiment on a graph of volume of O2 gas against time?

A
  • increases
  • most effective catalysts increase rate more effectively
  • results in a steeper line on the graph
  • the initial volume of the reactants is the same, so all lines would eventually flatten out at the same total volume of O2 (g) if you waited long enough
  • the MnO2 (s) - catalysed decomposition of hydrogen peroxide is used to produce oxygen in the lab

IGCSE Chemistry (18 decks)

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