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Chemistry > 3 Physical Chemistry > Flashcards

3 Physical Chemistry Flashcards

1
Q

what is an exothermic reaction

A

where heat and light energy is given out

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2
Q

what is an endothermic reaction

A

where heat energy is taken in (from the surroundings)

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3
Q

method to work out the effect in change of surface area of a solid on the rate of reaction

A
  1. Add dilute hydrochloric acid to a conical flask
  2. Use a delivery tube to connect this flask to an inverted measuring cylinder upside down in a water trough
  3. Add calcium carbonate chips into the conical flask and close the bung
  4. Measure the volume of gas produced in a fixed time using the measuring cylinder
  5. Repeat with different sizes of calcium carbonate chips (use 3g of small, medium, large chips)

results:
more gas will be produced from the smaller chips as they have a larger surface area

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4
Q

method to work out the effect in change of concentration of a solution on the rate of reaction

A
  1. Measure 50 cm3 of sodium thiosulfate solution into a conical flask
  2. Measure 5 cm3 of dilute hydrochloric acid into a measuring cylinder
  3. Draw a cross on a piece of paper and put it underneath the flask
  4. Add the acid into the flask and immediately start the stopwatch
  5. Look down at the cross from above and stop the stopwatch when the cross can no longer be seen
  6. Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate
    solution with water to dilute it)

results:
with an increased of the concentration the rate of reaction will increase meaning the cross will disappear quicker

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5
Q

method to work out the effect in change of temperature of a solution on the rate of reaction

A
  1. Dilute hydrochloric acid in a conical flask is heated to a set temperature using a water bath
    2 .Add a strip of magnesium to the HCl and start the stopwatch
  2. Stop the time when the magnesium fully dissolves
  3. Repeat at different temperatures and compare results

results:
With an increase in the temperature the magnesium will dissolve quicker

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6
Q

method to work out the effect of using a catalyst has on the rate of reaction

A
  1. Add hydrogen peroxide into a conical flask
  2. Use a delivery tube to connect this flask to a measuring cylinder upside down in water trough
  3. Add the catalyst (manganese(IV) oxide) into the conical flask and close the bung
  4. Measure the volume of gas produced in a fixed time using the measuring cylinder
  5. Repeat experiment without the catalyst of manganese(IV) oxide and compare results

results:
the catalyst will speed up the rate of reaction therefore the volume of gas produced will be greater when the catalyst is used

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7
Q

how does a catalyst affect the rate of reaction

A

the catalyst lowers the activation energy providing an alternate pathway for the reaction to take place
meaning the percentage of collisions with enough energy is higher
so there are more successful collisions per unit of time
increasing the rate of reaction

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8
Q

how does surface area affect the rate of reaction

A

with a larger SA rate of reaction increases because more surface area of the particles will be exposed to the other reactant
therefore more particles collide more frequently per unit of time
meaning there are more successful collisions per unit of time
and an increased rate of reaction

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9
Q

how does the temperature affect the rate of reaction

A

with higher temperature rate of reaction increases because the particles will have more kinetic energy
So the percentage of collisions with enough energy is higher
meaning more successful collisions per unit of time
increasing the rate of reaction

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10
Q

how does the concentration/pressure affect the rate of reaction

A

with a higher concentration/pressure the rate of reaction increases because there are more particles per given volume of mass
there for particles collide more frequently per unit of time
meaning there are more successful collisions per unit of time
increasing the rate of reaction

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11
Q

does the catalyst change the reaction

A

no the catalyst does not
the reaction is chemically unchanged at the end of the reaction

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12
Q

practical: investigate the effect of changing the surface area of marble chips and of changing the concentration of hydrochloric acid on the rate of reaction between marble chips and dilute hydrochloric acid

A
  1. Add dilute hydrochloric acid to a conical flask
  2. Use a delivery tube to connect this flask to an inverted measuring cylinder upside down in a water trough
  3. Add calcium carbonate chips into the conical flask and close the bung
  4. Measure the volume of gas produced in a fixed time using the measuring cylinder
  5. Repeat with different sizes of calcium carbonate chips (use 3g of small, medium, large chips)

results:
more gas will be produced from the smaller chips as they have a larger surface area

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13
Q

practical: investigate the effect of different solids on the catalytic decomposition of hydrogen peroxide solution

A
  1. Add hydrogen peroxide into a conical flask
  2. Use a delivery tube to connect this flask to a measuring cylinder upside down in water trough
  3. Add the catalyst (manganese(IV) oxide) into the conical flask and close the bung
  4. Measure the volume of gas produced in a fixed time using the measuring cylinder
  5. Repeat experiment with different catalysts and compare results
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14
Q

how to calculate heat energy change

A

Q=mcΔT
energy = mass x change in temp x specific heat capacity

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15
Q

how to calculate molar enthalpy change (ΔH)

A

ΔH = (Q / n) /1000 (to convert to kJ/mol)
enthalpy change = energy change / moles

Reactions where energy has been released / the temperature has increased are exothermic- this means your answers for enthalpy changes should be negative

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16
Q

describe simple calorimetry experiments for reactions in solution

A

can be used for:
neutralisation reactions
dissolving solids in water
displacement reactions

To calculate the amount of energy produced by a chemical reaction in solution we measure the temperature change when the solutions are mixed together
The solutions need to be mixed together in an insulated contain to prevent heat loss

A fixed volume of one reagent is added to the calorimeter and the initial temperature taken with a thermometer
An excess amount of the second reagent is added and the solution is stirred continuously
The maximum temperature is recorded and the temperature rise calculated using Q=mcΔT

17
Q

describe simple calorimetry experiments for combustion

A

The principle here is to use the heat released by a combustion reaction to increase the heat content of water

Method:
Measure a fixed volume of water into a copper can
Weigh the spirit burner containing a fuel using a balance
Measure the initial temperature of the water
Burn the fuel and stir the water
Wait for 30s and extinguish the flame
Record the final temperature of the water and re-weigh the spirit burner

18
Q

what is bond breaking

A

a endothermic process as it takes in energy to break down the bonds

19
Q

what is bond making

A

an exothermic process as energy is released when new bonds are formed

20
Q

how to use bond energies to calculate the enthalpy change during a chemical reaction

A

calculate the energy energy taken in from the reactants
calculate the energy released from making the bonds

enthalpy change = energy taken in - energy released

21
Q

how to draw an energy level diagram

A

energy on the y axis
progress of reaction on the x axis

for an endothermic:
reactants have less energy than products as energy is taken in so reactants line is below products. Arrow is pointing upwards

for an exothermic:
reactants have more energy than products as energy is given out. reactants line is above products and arrow points down

22
Q

practical: investigate temperature changes accompanying salts dissolving in water:

A

Using a measuring cylinder, place 25 cm3 of water into the calorimeter
Measure and record the temperature of the solution
Add 5g of salt and stir
Measure and record the highest temperature reached by the mixture
(endothermic)

23
Q

practical: investigate temperature changes accompanying neutralization reactions:

A

Using a measuring cylinder, place 25 cm3 of the NaOH solution into the calorimeter
Measure and record the temperature of the solution
Add 5 cm3 of the dilute HCl and stir
Measure and record the highest temperature reached by the mixture
(exothermic)

24
Q

practical: investigate temperature changes accompanying displacement reactions:

A

Using a measuring cylinder, place 25 cm3 of the copper sulfate into the calorimeter
Measure and record the temperature of the solution
Add magnesium and stir
Measure and record the highest temperature reached by the mixture
(exothermic)

25
Q

practical: investigate temperature changes accompanying combustion reactions:

A

Method:
Measure a fixed volume of water into a copper can
Weigh the spirit burner containing a fuel using a balance
Measure the initial temperature of the water
Burn the fuel and stir the water
Wait for 30s and extinguish the flame
Record the final temperature of the water and re-weigh the spirit burner
(exothermic)

26
Q

draw and explain reaction profile diagrams showing ΔH and activation energy

A

similar to energy level diagrams except instead of an arrow there is bump as they show how the energy changes as the reaction progresses

The difference in height between the energy of reactants and products represents the overall enthalpy change of a reaction

The initial increase in energy, from the reactants to the peak of the curve, represents the activation energy, Ea, required to start the reaction
The greater the initial rise then the more energy that is required to get the reaction going e.g., more heat needed

Chemistry (5 decks)

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