C4 Flashcards
What is the definition of Enthalpy of Formation?
The enthalpy change when one mole of a substance is produced from its constituent elements under standard conditions in their standard states.
What is the definition of Enthalpy of Combustion?
The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions.
State Hess’s law?
The enthalpy change of a reaction is independent of its route.
Enthalpy Change definition?
Heat energy change measured at constant pressure
Mean Bond Enthalpy definition?
Energy required to break a given covalent bond average over a range of compounds.
What is the standard state of Sulfur?
S(s)
Why is the enthalpy of combustion of Oxygen 0?
Because by definition, the enthalpy of formation is the formation of an element.
Why cannot the enthalpy change of a reaction be measured directly?
Because it is difficult to stop a solid from dissolving/Very difficult to measure the temperature rise of a solid/impossible to add a precise amount of water
Why is calculating enthalpy change using bond enthalpies less accurate than enthalpy of formation/combustion?
Because bond enthalpies are a mean value of lots of different compounds.
What would be the difference in enthalpy change of combustion if the products are in a liquid form instead of a gas form
It would be more exothermic as the water will release energy when it condenses.
