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TESTE DEIN WISSEN

know that the enthalpy change, ∆H, is the heat energy change measured at constant pressure and that standard conditions 

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TESTE DEIN WISSEN

are 100 kPa and a specified temperature, usually 298 K

Lösung ausblenden
TESTE DEIN WISSEN

Define the term standard molar enthalpy of formation, triangle H UFO (3)

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TESTE DEIN WISSEN

THe enthalpy change of the formation of 1 mole of the pure compound in its standard state from its pure elements under the standard conditions

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TESTE DEIN WISSEN

Suggest one reason why the students wished to prevent unreacted chlorine escaping into the atmosphere.

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TESTE DEIN WISSEN

Chlorine is toxic

Lösung ausblenden
TESTE DEIN WISSEN

Suggest one reason why the value of for enthalpy change cannot be measured directly. (1)

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TESTE DEIN WISSEN

It's very difficult to add the exact amount of water that prevent solid from dissolving, (like not too much to liquid, or not too less remain in dry solid, like need to be exact to hydrated solid)

Lösung ausblenden
TESTE DEIN WISSEN

Give a reason why a high pressure of 50 MPa is not normally used in the Haber Process. (1)

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TESTE DEIN WISSEN

It's too expensive to *maintain* (NOT rly generate

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TESTE DEIN WISSEN

Suggest why the value for the standard enthalpy of formation of liquid antimony, given in the table above, is not zero. (1)

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TESTE DEIN WISSEN

Sb has changed state, from solid to liquid, so not in its standard state.

https://www.scienceskool.co.uk/uploads/9/5/5/0/9550437/aqa_unit_2_2014_model_answers.pdf pg7

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TESTE DEIN WISSEN

Hence explain why 800K is referred to as a compromise temperature. (1)

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TESTE DEIN WISSEN

Balance between rate and yield (as lower temp, lower RoR; higher temp, lower yield so a balance has to be decided) :)

Lösung ausblenden
TESTE DEIN WISSEN

The alcohol 2-methylpropan-2-ol, (CH3)3COH, reacts to form esters that are used as flavourings by the food industry. The alcohol can be oxidised to produce carbon dioxide and water. A student carried out an experiment on a pure sample of 2- methylpropan-2-ol to determine its enthalpy of combustion. A sample of the alcohol was placed into a spirit burner and positioned under a beaker containing 50 cm3 of water. The spirit burner was ignited and allowed to burn for several minutes before it was extinguished. Suggest improvements to reduce errors due to heat loss. (4 marks)

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TESTE DEIN WISSEN

- Reduce the distance between the flame and the beaker

- Put a sleeve around the flame to protect from drafts

- Add a lid

- Use a copper calorimeter rather than a beaker

Lösung ausblenden
TESTE DEIN WISSEN

Deduce one reason why the method of extraction of antimony from a low-grade ore, described in part (a), is a low-cost process. Do not include the cost of the ore. (1)

Lösung anzeigen
TESTE DEIN WISSEN

Uses scrap iron OR as lower temperature is required for the antimony to react with carbon monoxide (not sure

https://www.scienceskool.co.uk/uploads/9/5/5/0/9550437/aqa_unit_2_2014_model_answers.pdf pg7

Lösung ausblenden
TESTE DEIN WISSEN

Give two reasons why an industrialist is unlikely to choose these reaction conditions. (2)

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TESTE DEIN WISSEN

- Big amount of energy required to maintain such high pressure (100MPa)

- High maintenance/insurance cost

- Strong pressure vessel/equipment required

Lösung ausblenden
TESTE DEIN WISSEN

State what is meant by the term mean bond enthalpy (2)

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TESTE DEIN WISSEN

The enthalpy change needed to break the covalent bond into gaseous atoms, averaged over different molecules. 

Lösung ausblenden
TESTE DEIN WISSEN

Explain the meaning of the term dynamic equilibrium

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TESTE DEIN WISSEN

RoFR = RoBR 

Concentration of the reactants and products remain constant in the equation.

Lösung ausblenden
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Q:

know that the enthalpy change, ∆H, is the heat energy change measured at constant pressure and that standard conditions 

A:

are 100 kPa and a specified temperature, usually 298 K

Q:

Define the term standard molar enthalpy of formation, triangle H UFO (3)

A:

THe enthalpy change of the formation of 1 mole of the pure compound in its standard state from its pure elements under the standard conditions

Q:

Suggest one reason why the students wished to prevent unreacted chlorine escaping into the atmosphere.

A:

Chlorine is toxic

Q:

Suggest one reason why the value of for enthalpy change cannot be measured directly. (1)

A:

It's very difficult to add the exact amount of water that prevent solid from dissolving, (like not too much to liquid, or not too less remain in dry solid, like need to be exact to hydrated solid)

Q:

Give a reason why a high pressure of 50 MPa is not normally used in the Haber Process. (1)

A:

It's too expensive to *maintain* (NOT rly generate

Mehr Karteikarten anzeigen
Q:

Suggest why the value for the standard enthalpy of formation of liquid antimony, given in the table above, is not zero. (1)

A:

Sb has changed state, from solid to liquid, so not in its standard state.

https://www.scienceskool.co.uk/uploads/9/5/5/0/9550437/aqa_unit_2_2014_model_answers.pdf pg7

Q:

Hence explain why 800K is referred to as a compromise temperature. (1)

A:

Balance between rate and yield (as lower temp, lower RoR; higher temp, lower yield so a balance has to be decided) :)

Q:

The alcohol 2-methylpropan-2-ol, (CH3)3COH, reacts to form esters that are used as flavourings by the food industry. The alcohol can be oxidised to produce carbon dioxide and water. A student carried out an experiment on a pure sample of 2- methylpropan-2-ol to determine its enthalpy of combustion. A sample of the alcohol was placed into a spirit burner and positioned under a beaker containing 50 cm3 of water. The spirit burner was ignited and allowed to burn for several minutes before it was extinguished. Suggest improvements to reduce errors due to heat loss. (4 marks)

A:

- Reduce the distance between the flame and the beaker

- Put a sleeve around the flame to protect from drafts

- Add a lid

- Use a copper calorimeter rather than a beaker

Q:

Deduce one reason why the method of extraction of antimony from a low-grade ore, described in part (a), is a low-cost process. Do not include the cost of the ore. (1)

A:

Uses scrap iron OR as lower temperature is required for the antimony to react with carbon monoxide (not sure

https://www.scienceskool.co.uk/uploads/9/5/5/0/9550437/aqa_unit_2_2014_model_answers.pdf pg7

Q:

Give two reasons why an industrialist is unlikely to choose these reaction conditions. (2)

A:

- Big amount of energy required to maintain such high pressure (100MPa)

- High maintenance/insurance cost

- Strong pressure vessel/equipment required

Q:

State what is meant by the term mean bond enthalpy (2)

A:

The enthalpy change needed to break the covalent bond into gaseous atoms, averaged over different molecules. 

Q:

Explain the meaning of the term dynamic equilibrium

A:

RoFR = RoBR 

Concentration of the reactants and products remain constant in the equation.

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