Topic 7 - Rates of Reaction and Energy Changes Flashcards

1
Q

Explain how reactions occur

A

for a reaction to happen:

  • reactant particles must collide
  • collisions must have enough energy

ACTIVATION ENERGY - minimum energy needed by reactant particles for reaction to happen, successful collisions have this

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2
Q

What increases rate of reaction?

A

greater the frequency of collisions, greater the rate of reaction

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3
Q

explain how temperature affects rate of reaction

A

rate INCREASES when temp increases bc particles gain energy and:

  • move faster
  • frequency collisions increase and
  • collision energy increases , more collisions successful
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4
Q

explain how concentration and pressure affects rate of reaction

A

rate INCREASES if concentration of dissolved reactant increases or pressure of gas reactant

  • more particles in same volume
  • successful collisions increases
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5
Q

explain how surface area:volume ratio affects rate of reaction

A

rate INCREASES when sa:v increases:

  • more reactant particles available
  • successful collisions increase
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6
Q

describe three features of a catalyst

A

catalysts - substances speed up rate without altering products.

unchanged chemically and in mass at end of reaction

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7
Q

explain how a catalyst works

A

catalysts provide alternative reaction pathway with lower activation energy

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8
Q

explain the use of enzymes

A

enzymes are BIOLOGICAL catalysts

used in the production of alcoholic drinks

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9
Q

explain the relationship between rate and time of reactions

A

the GREATER the rate, the LOWER the reaction time

  • fast reaction in short time eg combustion
  • slow reaction in long time eg rusting
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10
Q

explain effects of changes in heat energy

A
  • salts dissolving in water (endo & exo)
  • neutralisation reactions (endo & exo)
  • displacement reactions (exo)
  • precipitation reactions (endo & exo)
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11
Q

what is an endothermic reaction

A

heat energy TAKEN IN

reaction mixture or surroundings decrease in temperature

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12
Q

what is an exothermic reaction

A

heat energy GIVEN OUT

reaction mixture or surroundings increase in temperature

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13
Q

describe a method to measure temperature changes

A

thermometer, polystyrene cup, reaction mixture, lid with hole and beaker for support

beaker and air inside further insulation to reduce energy transfer

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14
Q

describe what happens in terms of bonding in endothermic vs exothermic

A

endothermic - breaking bonds (energy needed)
exothermic - making bonds (energy released)

bENDy mEXican

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15
Q

describe the overall heat energy trend in an endothermic reaction

A
  • less heat energy released forming bonds in products than required breaking bonds in reactants
  • positive energy change
  • reactant energy level lower than product
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16
Q

describe the overall heat energy trend in an exothermic reaction

A
  • more heat energy released forming bonds in products than required breaking bonds in reactants
  • reactant energy level greater than product
  • negative energy change
17
Q

explain the term activation energy

A

energy needed to start a reaction

18
Q

how to calculate energy change

A

energy change = total energy in - total energy out

if the final answer is a negative, reaction is exothermic
if positive, endothermic

19
Q

why does oxygen gas have an extremely low boiling point

A

weak intermolecular forces

20
Q

why do hotter acids react faster with calcium carbonate

A

higher temperature, quicker reaction

the particles move faster so more frequent collisions

21
Q

why does powdered calcium carbonate react faster with acid than big lumps?

A

higher surface to volume ratio, quicker reaction

more places for them to collide