All Flashcards
How do you calculate ΔHrxn using ΔHf values?
ΔHrxn = ΣnΔHf(products) - ΣmΔHf(reactants), where n and m are stoichiometric coefficients.
What is the first step to calculate ΔHrxn?
Write out the balanced chemical equation.
What is the second step to calculate ΔHrxn?
Identify the ΔHf values for each reactant and product.
What is the third step to calculate ΔHrxn?
Apply the formula: ΔHrxn = ΣnΔHf(products) - ΣmΔHf(reactants)
What is the fourth step to calculate ΔHrxn?
Make sure to pay attention to the stoichiometric coefficients in the balanced equation when applying the formula.
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.
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.