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IGCSE Chemistry > Energy changes > Flashcards

Energy changes Flashcards

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1
Q

Define the word exothermic

A

Gives out heat energy

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2
Q

Define the word endothermic

A

Take in heat energy

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3
Q

Give examples of types of reaction that are exothermic

A

Combustion
Neutralisation
Displacement

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4
Q

Give examples of types of reaction that are endothermic

A

Thermal decomposition

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5
Q

What is the symbol for enthalpy change

A

TriangleH

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6
Q

Define enthalpy change

A

The amount of heat energy taken in or given out during a reaction, per mole of reactant
i.e. the difference in energy between products and reactants

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7
Q

What are the units for enthalpy change

A

kJ/mol

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8
Q

For exothermic reactions is the enthalpy change negative or positive and why?

A

Negative

The reaction gives out energy so the products have less energy than the reactants

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9
Q

For endothermic reactions is the enthalpy change negative or positive and why?

A

Positive

The reaction takes in energy so the products have more energy than the reactants

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10
Q

Draw an energy level diagram for an exothermic reaction

A

__________
Reactants

                  \_\_\_\_\_\_\_\_\_
                   Products
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11
Q

Draw an energy level diagram for an endothermic reaction

A

X axis: Progress of reaction
Y axis: Energy

                      \_\_\_\_\_\_\_\_\_\_\_\_
                            products

_____________
reactants

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12
Q

Compare the energy stability in exothermic reactions

A

The products are more energetically stable than the reactants

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13
Q

Describe a practical to investigate temperature changes for displacement reactions

A
  1. Place the polystyrene cup into the beaker to keep it stable
  2. Measure out 25cm3 of hydrochloric acid solution using a measuring cylinder and pour this into the polystyrene cup
  3. Place the thermometer into the acid
  4. Carefully weigh out 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 solution quickly and stir the mixture gently with the thermometer
  7. Check the temperature regularly until the temperature stops rising. Record the maximum temperature
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14
Q

Describe a practical to investigate temperature changes for neutralisation reactions

A
  1. Place the polystyrene cup into the beaker to keep it stable
  2. Measure out 25cm3 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 25cm3 of sodium hydroxide using a measuring cylinder
  5. Record the starting temperature of the solution
  6. Add the magnesium to the solution quickly and stir the mixture gently with the thermometer
  7. Check the temperature regularly until the temperature stops rising. Record the maximum temperature
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15
Q

Describe a practical to investigate temperature changes for dissolving salts in water

A
  1. Place the polystyrene cup into the beaker to keep it stable
  2. Measure out 25cm3 of distilled water using a measuring cylinder and pour this into the polystyrene cup
  3. Place the thermometer into the acid
  4. Carefully weigh out 1.35g of ammonium nitrate into a weighing boat using a mass balance
  5. Record the starting temperature of the solution
  6. Add the magnesium to the solution quickly and stir the mixture gently with the thermometer
  7. Check the temperature regularly until the temperature stops rising. Record the maximum temperature
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16
Q

Describe a practical to investigate temperature changes for combustion reactions

A
  1. Measure out 100cm3 of water using a measuring cylinder and pour this into the conical flask
  2. Clamp the flask approximately 1cm above the spirit burner with the lid on
  3. Clamp the thermometer into the water so that. the bulb of the thermometer is submerged in the water but is not touching the bottom of the flask
  4. Record the mass of the spirit burner with the lid on
  5. Record the starting temperature of the solution
  6. Light the spirit burner and then move it under the conical flask.
  7. Allow the burner to heat the water until the temperature of the water rises by approximately 40C
  8. Move the burner out from under the conical flask and extinguish
  9. Check the temperature regularly until the temperature stops rising. Record the maximum temperature reached in the observations
  10. After cooling, record the mass of the burner
17
Q

What equations should you use for calculating enthalpy change of combustion reactions

A
  1. Q=mcdeltaT = J (mass of water)
  2. moles=mass/Mr (mass difference of spirit burner)
  3. (E/1000)/moles = kJ/mol
18
Q

Give possible sources of error in the combustion experiment (and explain)

A

1) Heat energy lost to surroundings
2) Incomplete combustion (less exothermic than complete)
3) Boiling/evaporating water - mass of water incorrect
4) Lid off spirit burner; fuel evaporate –> fuel mass burned bigger

19
Q

Describe the bonds in exothermic reactions

A

Bond making

Energy released

20
Q

Describe the bonds in endothermic reactions

A

Bond breaking

Requires energy

21
Q

Define bond energy

A

The amount of energy required to break a particular bond in kJ/mol

22
Q

How do you find out the total energy change for a chemical reaction?

A

DeltaH = total bond energy of reactants-total bond energy of products

23
Q

What determines whether a reaction is exothermic overall?

A

The energy released when the bonds form in the products is greater than the energy required to break bonds in the reactants

24
Q

What determines whether a reaction is endothermic overall?

A

The energy required to break bonds in the reactants is greater than the energy released when bonds form in the products

IGCSE Chemistry (10 decks)

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