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GCSE - Chemistry > Topic 7 - Rates Of Reaction And Energy Changes > Flashcards

Topic 7 - Rates Of Reaction And Energy Changes Flashcards

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1
Q

What is the equation for rate of reaction?

A

Rate of reaction = amount of reactant used/product formed / time

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2
Q

What units could be used for rate of reaction?

A

g/s
cm³/s
mol/s

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3
Q

How can you measure the rate of reaction when a gas is given off?

A

Measure time and collect gas in an upside down measuring cylider in trough of water/gas syringe to emasure vol of gas produced
Measure time and change in mass

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4
Q

How can you measure the rate of reaction when a precipitate is formed?

A

Put a black cross below a beaker containing one reactant. Time how long it takes for the cross to disappear after the secons reactant is added.

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5
Q

Why is using a precipitation method to investigate rate of reaction not very accurate?

A

Its subjective so people likely to disagree over exact pt cross no longer visible

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6
Q

How can you measure rate of reaction using a digital balance?

A

When a gas is produced as this will cause mass to decrease. The experiment can be carried out on a digital balance and rate of reaction can be calculated by recording the kass at regular time intervals.

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7
Q

What does ‘activation energy’ mean?

A

Minimum amount of energy required for a reaction to occur between 2 reacting particles

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8
Q

What must happen for a reaction to occur?

A

Particles must collide at the correct orientation with sufficient energy to react

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9
Q

In terms of particles, what 2 things could happen when the rate of reaction increases?

A

More frequent collisions

Energy of collisions increases

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10
Q

How can the rate of a reaction be increased?

A 
Increase temp
Increase concentration
Increase SA to vol ratio
Add catalyst
Increase pressure (for gases)
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11
Q

How does temp affect the rate of reaction?

A

Increased temp increases rate of reaction.
Reactants have more energy so more particles have energy above activation energy.
More sucessful collisions.
More frequent collisions - particles = more KE

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12
Q

How does SA affect rate of reaction?

A

Increasing SA increases rate of reaction

Bigger SA = more exposed particles v more frequent successful collisions

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13
Q

How does a catalyst affect the rate of reaction?

A

Increases the rate of reaction.
Provides an alternate reaction pathway w lower activation energy.
More particles will have sufficient energy to overcome the activation energy + react = more sucessful collisions in same time

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14
Q

How does concentration affect rate of reaction?

A

Increasing concentration increases rate of reaction.

More reacting oarticles in same vol = more frequent successful collisions.

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15
Q

How does pressure affect rate of a gaseous reaction?

A

Increasing pressure increases rate of reaction.

More reacting particles in same vol of gas /same no of particles in smaller vol = more frequent sucessful collisions

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16
Q

Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?

A

Use a digital balance to measure change in mass over a period of time (as carbon dioxide is released)

17
Q

Marble chips react woth hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could the rate of this reaction be increased?

A

Increase SA of marble chips by turning them into a powder.
Increase concentration of acid
Increase temp

18
Q

After completing an experiment, how can you find the rate of reaction using a graph?

A

Plot:
X axis: time
Y axis: amount of reactant used/product formed
Draw tangent to pt on graph and find gradient of line

19
Q

A graph showing time and amount of gas given off during an experiment has a steep gradient. What does this tell you about the rate of reaction?

A

Fast rate of reaction

20
Q

A graph is plotted to show time and the amount of gas given off during a reaction. Describe the shape of the curve.

A

Initially curve is very steep as rate of reaction = fast at start.
Curve becomes less steep as reactants get used up because fewer successful collisions occuring.
At end, graph is flat line - all reactants have been turned into products.

21
Q

What is a catalyst?

A

Substance which speeds up the rate of a reaction without being chemically changed at end

22
Q

How does a catalyst speed up the rate of a reaction?

A

Provides an alternate reaction pathway w lower activation energy

23
Q

What are enzymes?

A

Act as biological catalysts that increase the rate of reactions in living cells.

24
Q

Which enzyme is used to produce ethanol from glucose?

A

Yeast

25
Q

What do the terms exothermic and endothermic mean?

A

Exothermic - reaction that gives out energy

Endothermic - reaction that takes in heat energy

26
Q

Are neutralisation reactions endonor exothermic?

A

Exothermic

27
Q

Are displacement reactions endo or exothermic?

A

Can be either

28
Q

Is a salt dissolving in water exo or endothermic?

A

Can be either

29
Q

Are precipitation reactions exo or endothermic?

A

Exothermic

30
Q

How could you measure the temp change of a neutralisation reaction?

A

Measure initial temp of solutions.
Mix both reactants in polystyrene cup.
Record highest temp reached.
Calculate temp change.

31
Q

When measuring the temp change of a reaction, heat loss means that measurements may be inaccurate. How could heat loss be minimised during an experiment?

A

Use polystyrene cup
Place reaction cup in beaker full of cotton wool
Lid on reaction cup

32
Q

In terms of bond energies, what happens during a chemical reaction? Describe exothermic and endothermic reactions in terms of bonds breaking/forming

A

Energy needed to break bonds and released when bonds are made.
Exothermic: energy released from breaking bonds = bigger than energy used to make bonds
Endothermic: energy released in forming new bond is greater than energy used to break old bonds

33
Q

What 2 types of reaction are exothermic?

A

Combustion

Neutralisation

34
Q

Give an example of an endothermic reaction

A

Thermal decomposition

Photosynthesis

35
Q

How can energy change of a reaction be calculated from bond energies?

A

Energy change (kJ mol⁻¹) = totak energy of bonds broken - total energy of bonds made

36
Q

If the energy change of a reaction is negative, is the reaction exothermic or endothermic?

A

Exothermic - energy is lost to surroundings

37
Q

What is a reaction profile?

A

Graph showing relative energies of reactants and products, as well as the activation energy of a reaction

GCSE - Chemistry (8 decks)

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