All Flashcards
What is the difference between H2O(l) and H2O(g) when calculating ΔHrxn?
They have different ΔHf values. Always use the value corresponding to the correct state.
What is the standard enthalpy of formation (ΔHf)?
The enthalpy change when one mole of a compound is formed from its elements in their most stable state at standard conditions (25°C and 1 atm).
What are standard conditions for enthalpy of formation?
25°C (298 K) and 1 atm.
What is meant by 'most stable state'?
The form of an element that is most stable at standard conditions (e.g., O2(g), C(s, graphite)).
What is the ΔHf of an element in its standard state?
Zero.
Define ΔHrxn.
The enthalpy change for a chemical reaction.
What is the effect of using the wrong state symbol (e.g., H2O(g) instead of H2O(l))?
It will lead to an incorrect ΔHrxn calculation.
What is the effect of not balancing the chemical equation correctly?
Incorrect stoichiometric coefficients will lead to an incorrect ΔHrxn calculation.
What is the effect of a catalyst on ΔH°?
The value of ΔH° would not be affected because a catalyst does not change the enthalpy of the reaction, it only changes the rate.