Chemistry > Energetics > Flashcards

Energetics Flashcards

(21 cards)

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1
Q

What is a exothermic reaction

A

Chemical reaction in which heat energy is given out to the surroundings

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2
Q

Define an endothermic reaction

A

Chemical reaction in which heat energy is taken in from the surroundings

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3
Q

What types of reactions are exothermic

A

-displacement
-combustion
-neutralisation

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4
Q

What types of reactions are endothermic

A

-thermal decomposition

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5
Q

How do you calculate the heat energy change

A

Heat energy change = mass x specific heat capacity x temperature change
Q= m x c x triangle T

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6
Q

How do you calculate the molar enthalpy change

A
  1. Calculate energy transfer with m x c x triangle T
  2. Calculate the number of moles in the element
  3. Calaulcatw the enthrall change by doing -energy transfer divided by number of moles
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7
Q

What is the unit for molar enthalpy change

A

J/mol or kJ/mol

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8
Q

Is bond breaking endothermic or exothermic

A

Endothermic as you must put energy in to break the chemical bonds

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9
Q

Is bond making endothermic and exothermic

A

Exothermic as energy is released when new bonds form

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10
Q

How do you use bond energies to calculate the enpathly change

A
  1. Calculate Energy put in to break bonds
  2. Calculate energy released by new bonds
  3. Calculate overall energy change by breaking energy - making energy
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11
Q

What is the method of core prac 9: investigate temperature changes accompanying various types of reaction - displacement

A
  1. Place a polystyrene cup into a beaker to keep it stable
  2. Measure out a volume (e.g 25cm^3) of hydrochloric acid solution using a measuring cylinder and pour this into the polystyrene cup
  3. Place the thermometer into the acid
  4. Carefully weight out a mass (e.g 0.3g) of magnesium powder into a weighing boat using a mass balance
  5. Record the starting temperature of the solution
  6. Add the magnesium to the acid quickly and store the mixture gently using a thermometer
  7. Check the temperature regularly until it stops rising. Record the maximum temperature
    -to calculate the heat energy change multiply the volume of hydrochloric acid (e,g 25cm^3) by the heat capacity (4.2) by the temperature change
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12
Q

What is the method of core prac 9: investigate the temperature changes accompanying various types of reaction - neutralisation

A
  1. Place a polystyrene cup into a beaker to keep it stable
  2. Measure out a volume (e.g 25cm^3) of hydrochloric acid solution using a measuring cylinder and pour this into the polystyrene cup
  3. Place the thermometer into the acid
  4. Measure out the same volume of sodium hydroxide solution as the acid (e.g 25cm^3)
  5. Record the starting temperature of the solution
  6. Add the sodium hydroxide solution to the acid quickly and store the mixture gently using a thermometer
  7. Check the temperature regularly until it stops rising. Record the maximum temperature
    -to calculate the heat energy change add both the volumes of the acid (hydrochloric acid) and alkali (sodium hydroxide) (e.g 25+25) and multiply that by the heat capacity (4.2) and the temperature change
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13
Q

What is the method of core practical 9: investigating temperature changes accompanying various types of reaction- dissolving salts

A
  1. Place a polystyrene cup into a beaker to keep it stable
  2. Measure out a volume (e.g 25cm^3) of distilled water using a measuring cylinder and pour this into the polystyrene cup
  3. Place the thermometer into the acid
  4. Carefully weight out a mass (e.g 1.50g) of potassium chloride into a weighing boat using a mass balance
  5. Record the starting temperature of the solution
  6. Add the potassium chloride to the distilled water quickly and store the mixture gently using a thermometer
  7. Check the temperature regularly until it stops rising. Record the maximum temperature
    -to calculate the heat energy change multiply the volume of the distilled water (e,g 25cm^3) by the heat capacity (4.2) and then by the change in temperature (e.g -3)
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14
Q

What is the method of core prac 9: investigating temperature changes accompanying various types of reaction- combustion

A
  1. Measure out 100cm^3 of water using a measuring cylinder and pour this into the copper calorimeter
  2. Collect a spirit burner containing the alcohol and place on a heatproof mat
  3. Clamp the calorimeter approximately 1cm above the spirit burner
  4. Place the thermometer into the water and record its starting temp
  5. Record the mass of the spirit burner with its lid on
  6. Place the spirit burner onto the heatproof mat, remove its lid and quickly light it and place it under the calorimeter
  7. Allow the burner to heat the water until the temperature of the water rises by approximately 40°C. While the water is being heated, gently stir it with the thermometer
  8. Move the burner out from under the calorimeter and replace the lid to extinguish the flame
  9. Check the temperature until it stops rising and record the maximum temp reached
  10. Record the new mass of the spirit burner
  11. Repeat with the other alchohols
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15
Q

How do you calculate the molar enthalpy change for core prac 9: combustion

A

-calculate the energy change using the volume of the water (e.g 100cm^3) by the heat capacity (e.g 4.2) by the change in temperature (e.g 40°)
-calculate the number of moles burned by the alcohol by dividing the mass of alcohol burned (subtract final from initial mass) by the mr of the alcohol
-divide the minus of the energy change (e,g -20,000) by the number of moles burned
-the answer should be a minus number

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16
Q

In core prac 9: combustion why may the values calculated be inaccurate

Study These Flashcards
A

-heat loss to surroundings
-incomplete combustion occurs which is less exothermic than complete combustion
-come fuel evaporated from the wick after the lid was taken off

17
Q

In core prac 9: combustion how can accuracy be improved

Study These Flashcards
A

-insulate the calorimeter around the sides
-use a calorimeter with a lid
-use a form of draught excluder e.g heatproof mats

18
Q

In core prac 9: displacement wheat would happen if double the volume of hydrochloric acid (50cm^3) was used

Study These Flashcards
A

The temperate change would remain the same as the volume of hydrochloric acid does not affect the experiment as it is not limiting

19
Q

In core prac 9: displacement, neutralisation and dissolving salts why is a polystyrene cup used rather than a beaker and how can accuracy be improved

Study These Flashcards
A

-it is an insulator so reduced heat loss to the surroundings
-insulate the cup more
-place a lid on the cup

20
Q

In core prac nine: neutralisation what is a safety precaution needed

Study These Flashcards
A

-safety goggles as sodium hydroxide solution is used

21
Q

Draw energy level diagrams/ profiles

Chemistry
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