Science Flashcards
(97 cards)
1
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Rate of Reaction
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2
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The rate of a reaction means how quickly reactants are turned into the
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3
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products.
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4
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2H2 + 02-
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→ 2H20
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reactants
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products
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If this happens quickly then you have a high rate of reaction
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if it takes a long
9
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time then you have a slow rate of reaction.
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10
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An example of a slow reaction could be rusting
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11
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An example of a fast reaction could be an explosion.
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12
Q
Calculating the Rate of Reaction
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13
Q
The rate of a reaction can be found by the equation below.
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14
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mean rate of reaction = quantity of reactant used
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15
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time taken
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16
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mean rate of reaction = quantity of product formed
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17
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time taken
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18
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This is the same as saying on a graph like the one shown that
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19
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the change in Y / the change in X = the rate of a reaction.
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20
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70
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stopped
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22
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60 -
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23
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50 -
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40
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slowing
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down
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rolume of gas
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20
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10 -
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fastest
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The line is curved.
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This means that
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the rate of
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reaction changes
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as it progresses.
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0 *
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20
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Collision theory
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Why do things react in the first place?
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Things will only react if the particles collide with
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enough energy to cause a effective collision. This
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is best illustrated in the diagram to the right. A
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faster reaction will have a higher frequency of
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collisions with sufficient energy
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Factors effecting the rate of a reaction
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There are several factors that can effect the rate of a
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chemical reaction
however it essentially boils down to
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increasing the amount of successful collision.
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These factors are.
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Temperature
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The hotter the particles are
the faster they move and
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therefore the frequency of successful collisions is greater.
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Pressure and concentration
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More particle in the same space means that collisions
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happen with greater frequency.
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Surface area
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If there are more particles exposed to the reactants then
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the frequency of successful collision is greater.
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Catalysis
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See the box below.
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Catalysts
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Catalysts are substances that speed up the rate of a
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reaction without being used up themselves. They work by
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lowering the activation energy. This is the amount of
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energy needed to get a reaction going. Just like striking a
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match
you need to put some energy into it
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not just burst into flames by itself. The graph to the right
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shows an energy profile of a catalysed reaction when
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compared to the same one that is not catalysed.
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Low energy collision
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No reaction
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High energy collision
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+
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More COz formation
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Reversible Reactions
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Reversible reaction are ones that will react
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in both directions.
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This means that as quickly as products are
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formed they can be turned back into
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reactants.
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Reversible reactions are identifiable by the
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arrow in the middle of the reaction.
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N2 + 3H2
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2NH3
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energy
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without catalyst
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Ea (without)
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with catalyst
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reactants
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1100
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11901
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140
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160 180
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time (s)
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products
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reaction profile
