physical chemistry

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17 Terms

1

How is the rate of a reaction calculated?

rate = amount of reactant used / time

OR

amount of product formed / time

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2

Describe how to carry out an experiment to measure the rate of reaction when a precipitate is formed

- Example: Sodium thiosulfate solution and dilute hydrochloric acid react together to form a

precipitate of sulfur

- Place 20 cm3 of sodium thiosulfate solution and 20 cm3 of water in a conical flask

- Add 10 cm3 of dilute hydrochloric acid to the flask

- Place the flask on a piece of paper marked with a black X

- Time how long it takes before the X can no longer be seen

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3

Describe how to carry out an experiment to measure the rate of reaction when a gas is produced

- Example: The decomposition of hydrogen peroxide (H2O2) into H2O and O2

- Place a known mass of H2O2 in a conical flask

- Seal flask with a bung attached to a gas syringe

- Time how long it takes for 100cm3 of oxygen to be collected

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4

Describe how to carry out an experiment to measure the rate of reaction from the change in mass of a solid

- Example: Reaction of marble chips (CaCO3) with dilute hydrochloric acid

- Place 50cm3 HCl into a conical flask. Place the flask on a balance

- Add marble chips and note the starting mass

- Place cotton wool in the neck of the flask to stop acid spraying out

- Measure the mass of carbon dioxide lost at intervals

- Plot a graph of the results

- Repeat changing one variable only

- e.g. temperature, surface area, concentration of HCl

<p>- Example: Reaction of marble chips (CaCO3) with dilute hydrochloric acid</p><p>- Place 50cm3 HCl into a conical flask. Place the flask on a balance</p><p>- Add marble chips and note the starting mass</p><p>- Place cotton wool in the neck of the flask to stop acid spraying out</p><p>- Measure the mass of carbon dioxide lost at intervals</p><p>- Plot a graph of the results</p><p>- Repeat changing one variable only</p><p>- e.g. temperature, surface area, concentration of HCl</p>
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5

What effect does a higher temperature have on the rate of reaction?

- Rate increases

- Particles have greater kinetic energy

- More collisions have energy greater than activation energy

- More successful collisions occur per second

<p>- Rate increases</p><p>- Particles have greater kinetic energy</p><p>- More collisions have energy greater than activation energy</p><p>- More successful collisions occur per second</p>
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6

What effect does increasing the concentration have on the rate of reaction?

- Rate increases

- More particles in the same volume

- Collisions occur more frequently

<p>- Rate increases</p><p>- More particles in the same volume</p><p>- Collisions occur more frequently</p>
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7

What effect does increasing the pressure of a gas have on the rate of reaction?

- Rate increases

- More particles in the same volume

- Collisions occur more frequently

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8

What effect does increasing the surface area have on the rate of reaction?

- Rate increases

- Collisions occur more frequently

<p>- Rate increases</p><p>- Collisions occur more frequently</p>
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9

Define catalyst

- A substance that increases the rate of reaction

- Chemically unchanged at the end of the reaction

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10

How does a catalyst work?

- Speeds up the rate of reaction without being used up

- Provides alternative reaction pathway with lower activation energy

<p>- Speeds up the rate of reaction without being used up</p><p>- Provides alternative reaction pathway with lower activation energy</p>
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11

Which variables should be controlled when investigating the effect of temperature on the rate of a reaction?

- Concentration of reactants

- Volume of reactants

- Surface area (if using a solid)

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12

Which variables should be controlled when investigating the effect of concentration on the rate of a reaction?

- Concentration of all reactants other than the one being investigated

- Volume of reactants

- Surface area (if using a solid)

- Temperature

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13

Which variables should be controlled when investigating the effect of surface area on the rate of a reaction?

- Concentration of reactants

- Volume of reactants

- Temperature

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14

Which variables should be controlled when investigating the effect of a catalyst on the rate of a reaction?

- Concentration of reactants

- Volume of reactants

- Temperature

- Surface area

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15

What does this ⇌ arrow represent?

- Reaction is reversible

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16

Describe the dehydration of copper (II) sulfate crystals

- Heat blue (hydrated) copper (II) sulfate crystals

- Blue crystals turn to white powder

- Because water is lost i.e. water of crystallisation is lost

- White anhydrous copper (II) sulfate is formed

- Add water and blue (hydrated) copper (II) sulfate crystals form

- Reaction is reversible

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17

Describe the heating of ammonium chloride

- Place white crystals of ammonium chloride in bottom of boiling tube

- Heat using Bunsen burner

- When ammonium chloride is heated it splits into ammonia and hydrogen chloride

- White crystals disappear from bottom of tube

- Reaction reverses when conditions change from hot to cold higher up tube

- White crystals reform higher up

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