3/22/25, 11:58 BTEC Applied Science - Unit 5 - Chemistry - Enthalpy Flashcards |
AM
BTEC APPLIED SCIENCE - UNIT 5 - CHEMISTRY – ENTHALPY EXAM
QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS
Terms in this set (15)
(delta)U + P(delta)V
What is enthalpy change defined as? (delta)U = change in internal energy
P = pressure
(delta)V = change in vol.
What happens to the enthalpy value in The enthalpy value will be negative as the enthalpy of products is lower than that
exothermic conditions? of the reactants. (energy out).
What happens to the enthalpy value in The enthalpy value is positive as the enthalpy of products is higher than that of the
endothermic conditions? reactants (energy in).
They are able to vary between oxidation states so are able to be used in a range of
Why are transition metal complexes used reaction pathways. They reduce the activation energy and provide an
as catalysts? alternative pathway for the reaction.
The transition metal will also return to its original oxidation state so it is unchanged.
The costs of energy are high.
So, heat from exothermic reactions is captured and released to other parts of the
factory.
Heat Energy in Industry
The heat is therefore not wasted and is used to speed up reactions.
Using catalysts means that reactions are carried out at a lower temp to use less
energy.
the enthalpy change when all reactants and products are in their standard states.
What is standard enthalpy change?
As well as the surrounding conditions.
Pressure = 100KPa
What are the standard conditions for
Conc of Solutions = 1mol dm-3
enthalpy?
Temp = 298K
0K = -273C
273K = 0C
The Kelvin Temp Scale
K --> C = (-273)
C --> K = (+273)
The enthalpy change that occurs when 1 mole of a substance is formed from its
Standard Enthalpy of Formation
elements in standard state under standard conditions.
The enthalpy change that occurs when one mole of a substance in its standard
Standard Enthalpy of Combustion
states is completely burnt in oxygen under standard conditions.
2 processes occur when solids are dissolved in water.
- The ions break off the lattice which requies energy so is ENDOTHERMIC
Dissolving Ionic Compounds in Enthalpy
Change of Hydration - The new seperate ions form electrostatic attractions which have slightly
charged H2O molecules.
- This process used energy so is EXOTHERMIC
- The 2nd process compensates for the energy needed in the 1st process.
The enthalpy change that occurs when 1 mole of gaseous ions are dissolved in water
Standard Enthalpy Change of Hydration
to make an infinitely dilute solution.
1/
2
AM
BTEC APPLIED SCIENCE - UNIT 5 - CHEMISTRY – ENTHALPY EXAM
QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS
Terms in this set (15)
(delta)U + P(delta)V
What is enthalpy change defined as? (delta)U = change in internal energy
P = pressure
(delta)V = change in vol.
What happens to the enthalpy value in The enthalpy value will be negative as the enthalpy of products is lower than that
exothermic conditions? of the reactants. (energy out).
What happens to the enthalpy value in The enthalpy value is positive as the enthalpy of products is higher than that of the
endothermic conditions? reactants (energy in).
They are able to vary between oxidation states so are able to be used in a range of
Why are transition metal complexes used reaction pathways. They reduce the activation energy and provide an
as catalysts? alternative pathway for the reaction.
The transition metal will also return to its original oxidation state so it is unchanged.
The costs of energy are high.
So, heat from exothermic reactions is captured and released to other parts of the
factory.
Heat Energy in Industry
The heat is therefore not wasted and is used to speed up reactions.
Using catalysts means that reactions are carried out at a lower temp to use less
energy.
the enthalpy change when all reactants and products are in their standard states.
What is standard enthalpy change?
As well as the surrounding conditions.
Pressure = 100KPa
What are the standard conditions for
Conc of Solutions = 1mol dm-3
enthalpy?
Temp = 298K
0K = -273C
273K = 0C
The Kelvin Temp Scale
K --> C = (-273)
C --> K = (+273)
The enthalpy change that occurs when 1 mole of a substance is formed from its
Standard Enthalpy of Formation
elements in standard state under standard conditions.
The enthalpy change that occurs when one mole of a substance in its standard
Standard Enthalpy of Combustion
states is completely burnt in oxygen under standard conditions.
2 processes occur when solids are dissolved in water.
- The ions break off the lattice which requies energy so is ENDOTHERMIC
Dissolving Ionic Compounds in Enthalpy
Change of Hydration - The new seperate ions form electrostatic attractions which have slightly
charged H2O molecules.
- This process used energy so is EXOTHERMIC
- The 2nd process compensates for the energy needed in the 1st process.
The enthalpy change that occurs when 1 mole of gaseous ions are dissolved in water
Standard Enthalpy Change of Hydration
to make an infinitely dilute solution.
1/
2
