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Chemistry > C7 Rates of reaction > Flashcards

C7 Rates of reaction Flashcards

1
Q

What are enzymes?

A

biological catalysts

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2
Q

What are enzymes used in the production of?

A

alcoholic drinks

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3
Q

What is a reaction profile graph?

A

a graph that shows how the energy in a reaction changes as the reaction progresses

y axis - energy
x axis - progression of reaction

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4
Q

What does a reaction profile start and end with?

A
  • starts with energy level of reactants

- ends with energy level of products

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5
Q

What are the two ways you can calculate overall energy change?

A

overall evenergy change
= reactant energy - products energy
= bond breaking energies - bond forming energies

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6
Q

What will be the energy levels of reactants and products in an exothermic reaction?

A
  • reactants have more energy than products

- energy is being released to the surroundings

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7
Q

What will be the energy levels of reactants and products in an endothermic reaction?

A
  • reactants have less energy than products

- energy is being absorbed from the surroundings

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8
Q

What is activation energy?

A

minimum amount if energy particles need when they collide in order to react

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9
Q

What are the factors that affect the rate of reaction?

A
  • temperature
  • concentration of dissolved reactants
  • pressure of gas reactants
  • surface area of solid reactants
  • using a catalyst
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10
Q

How does temperature affect particle collision? (therefore affecting RoR)

A
  • as temp increases, RoR increases
  • at higher temp particles have more kinetic energy
  • move faster and more likely to collide with other particles
  • when particles collide they do so with energy
  • so the frequency of successful collisions increases
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11
Q

How does concentration affect particle collision? (therefore affecting RoR)

A
  • as conc of a dissolved reactant increases, RoR increases
  • higher conc, more particles in the same amount of space
  • frequency of collisions increases
  • so particles are more likely to react
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12
Q

How does surface area affect particle collision? (therefore affecting RoR)

A
  • as the surface area of a solid increases, RoR increases
  • increased area for particles to collide with
  • frequency of collisions increases
  • greater chance of reaction
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13
Q

How will using a catalyst affect rate of reaction?

A
  • using a catalyst lowers the activation energy
  • more particles have the minimum energy needed for a reaction to occur when they collide
  • increases RoR
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14
Q

What are the properties of catalysts?

A
  • do not proudce more product
  • do not get used up in reaction
  • do not get chemically changed
  • small amounts will catalyse large amounts of reactants
  • save time in industry, reducing energy use and thus reduces fuel use and pollution
  • enzymes are biological catalysts
  • reusable
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15
Q

What are the two ways of calculating the mean rate of reaction?

A

mean RoR = quantity of reactant used/time

mean RoR = quantity of product used/time

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16
Q

What do steep/flatter/horizontal lines on a reaction profile tell us?

A
  • steep: reaction fastest
  • flatter: slower RoR
  • horizontal: reaction stopped
17
Q

How do you calculate RoR from a graph?

A

RoR = gradient=change in y/change in x

  • draw a tangent to given point
  • pick two points on the tangent
  • calculate the gradient
18
Q

When a chemical reaction occurs, energy will be __________ to or from the ________ energy store if the products depending on the ________ energy store of the reactants.

A
  • transferred
  • chemical
  • chemical
19
Q

If the products in a chemical reaction transfer thermal emergy to the surroundings, the temperature of the surroundings will ________.

A

increase

20
Q

If the products in a chemical reaction transfer thermal emergy from the surroundings, the temperature of the surroundings will ________.

A

decrease

21
Q

Exothermic reactions ________ thermal energy ____ the surroundings. The temperature of the surrounding will ________.

A
  • release
  • into
  • increase
22
Q

Endothermic reactions ________ thermal energy ____ the surroundings. The temperature of the surrounding will ________.

A
  • absorb
  • from
  • decrease
23
Q

How can we experiment to test if a reaction is endo- or exo- thermic?

A
  • use a measuring cylinder to measure 50cm^3 of water
  • pour the water into the polystyrene cup
  • put the polystyrene cup into a beaker that has been padded with cotton wool
  • measure the initial temperature of the water
  • add the solid and stir gently for 5 mins
  • measure the final temperature of solution
  • work out is the temperature increased or decreased
24
Q

How can we improve method of measuring whether a reaction is endo- or exo- thermic?

A

-add a lid
–to reduce heat transfer to the surroundings

-add cotton wool to beaker
–to reduce heat transfer to surroundings

25
Q

What does the amount of energy released or absorbed in a reaction depend on?

A

how much reactant is used

26
Q

What do we need to do to get bonds between molecules to break?

A

supply energy

27
Q

What happens when new bonds are formed?

A

energy is released

28
Q

Bond breaking is a _________ process and why?

A
  • endothermic
  • energy us being absorbed from surroundings
  • to break existing bonds
29
Q

Bond forming is a _________ process and why?

A
  • exothermic
  • energy is being released to the surroundings
  • when new bonds are made
30
Q

What happens in exothermic reactions?

A
  • bonds formed
  • energy released > energy used to break old bonds
  • leftover energy released to surroundings
  • temperature of the surroundings increases
31
Q

What happens in endothermic reactions?

A
  • bond breaking
  • energy needed to break bonds > energy released when new bonds are formed
  • the extra energy needed is absorbed from the surrounding
  • temperature of surroundings decreases
32
Q

What do positive and negative energy changes indicate?

A

negative - exothermic

positive - endothermic

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