3.1.4 Energetics, A Level Chemistry, AQA
questions with complete solutions.
What is enthalpy change? - ANS.Heat energy transferred in a reaction at constant
pressure
What are standard conditions for enthalpy change? - ANS.100kPa and stated
temperature (normally 25 degrees celcius)
What values of deltaH do exothermic reactions have? - ANS.Negative (less than 0)
What values of deltaH do endothermic reactions have? - ANS.Positive (more than 0)
What do exothermic reactions do with energy? - ANS.Give out energy
What do endothermic reactions do with energy? - ANS.Absorb energy
Are oxidation reactions endo or exothermic? - ANS.Exothermic
Is combustion endo or exothermic? - ANS.Exothermic
Are thermal decomposition reactions endo or exothermic? - ANS.Endothermic
Is photosynthesis endo or exothermic? - ANS.Endothermic
What happens to reactant bonds? - ANS.They are broken
, What happens to product bonds? - ANS.They are formed
Which bonds are broken: reactant or product bonds? - ANS.Reactant
Which bonds are formed: reactant or product bonds? - ANS.Product
Is energy taken in or released when you break bonds? - ANS.Taken in
Is bond breaking endo or exothermic? - ANS.Endothermic
What values of deltaH does bond breaking have? - ANS.Positive (more than 0)
How does bond breaking energy change as the bond strength increases? - ANS.It
takes more energy to break
Is energy taken in or released when you make bonds? - ANS.Released
Is bond making endo or exothermic? - ANS.Exothermic
What values of deltaH does bond making have? - ANS.Negative (less than 0)
How does bond making energy change as the bond strength increases? - ANS.They
release more energy when formed
If you need more energy to break bonds than is released when bonds are made, what
values of deltaH do you get? - ANS.Positive (more than 0)
If you need less energy to break bonds than is released when bonds are made, what
values of deltaH do you get? - ANS.Negative (less than 0)
What is bond enthalpy? - ANS.The energy required to break bonds
What is the mean bond enthalpy? - ANS.The average energy needed to break a
certain type of bond, over a range of compounds
Why are mean bond enthalpies not exact? - ANS.They are an average of energies
needed to break the bond over a range of compounds
Why may a mean bond enthalpy in a data book be different from the mean bond
enthalpy in a specific molecule? - ANS.The mean bond enthalpy in the data book is
the average for a bigger range of molecules than just the specific molecule.
Why are mean bond enthalpies always positive? - ANS.Breaking bonds is always
endothermic
questions with complete solutions.
What is enthalpy change? - ANS.Heat energy transferred in a reaction at constant
pressure
What are standard conditions for enthalpy change? - ANS.100kPa and stated
temperature (normally 25 degrees celcius)
What values of deltaH do exothermic reactions have? - ANS.Negative (less than 0)
What values of deltaH do endothermic reactions have? - ANS.Positive (more than 0)
What do exothermic reactions do with energy? - ANS.Give out energy
What do endothermic reactions do with energy? - ANS.Absorb energy
Are oxidation reactions endo or exothermic? - ANS.Exothermic
Is combustion endo or exothermic? - ANS.Exothermic
Are thermal decomposition reactions endo or exothermic? - ANS.Endothermic
Is photosynthesis endo or exothermic? - ANS.Endothermic
What happens to reactant bonds? - ANS.They are broken
, What happens to product bonds? - ANS.They are formed
Which bonds are broken: reactant or product bonds? - ANS.Reactant
Which bonds are formed: reactant or product bonds? - ANS.Product
Is energy taken in or released when you break bonds? - ANS.Taken in
Is bond breaking endo or exothermic? - ANS.Endothermic
What values of deltaH does bond breaking have? - ANS.Positive (more than 0)
How does bond breaking energy change as the bond strength increases? - ANS.It
takes more energy to break
Is energy taken in or released when you make bonds? - ANS.Released
Is bond making endo or exothermic? - ANS.Exothermic
What values of deltaH does bond making have? - ANS.Negative (less than 0)
How does bond making energy change as the bond strength increases? - ANS.They
release more energy when formed
If you need more energy to break bonds than is released when bonds are made, what
values of deltaH do you get? - ANS.Positive (more than 0)
If you need less energy to break bonds than is released when bonds are made, what
values of deltaH do you get? - ANS.Negative (less than 0)
What is bond enthalpy? - ANS.The energy required to break bonds
What is the mean bond enthalpy? - ANS.The average energy needed to break a
certain type of bond, over a range of compounds
Why are mean bond enthalpies not exact? - ANS.They are an average of energies
needed to break the bond over a range of compounds
Why may a mean bond enthalpy in a data book be different from the mean bond
enthalpy in a specific molecule? - ANS.The mean bond enthalpy in the data book is
the average for a bigger range of molecules than just the specific molecule.
Why are mean bond enthalpies always positive? - ANS.Breaking bonds is always
endothermic
