How do you calculate ΔHrxn using ΔHf values?

ΔHrxn = ΣnΔHf(products) - ΣmΔHf(reactants), where n and m are stoichiometric coefficients.

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How do you calculate ΔH<sub>rxn</sub> using ΔH<sub>f</sub> values?
ΔH<sub>rxn</sub> = ΣnΔH<sub>f</sub>(products) - ΣmΔH<sub>f</sub>(reactants), where n and m are stoichiometric coefficients.
What is the first step to calculate ΔH<sub>rxn</sub>?
Write out the balanced chemical equation.
What is the second step to calculate ΔH<sub>rxn</sub>?
Identify the ΔH<sub>f</sub> values for each reactant and product.
What is the third step to calculate ΔH<sub>rxn</sub>?
Apply the formula: ΔH<sub>rxn</sub> = ΣnΔH<sub>f</sub>(products) - ΣmΔH<sub>f</sub>(reactants)
What is the fourth step to calculate ΔH<sub>rxn</sub>?
Make sure to pay attention to the stoichiometric coefficients in the balanced equation when applying the formula.
What is the standard enthalpy of formation (ΔH<sub>f</sub>)?
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., O<sub>2</sub>(g), C(s, graphite)).
What is the ΔH<sub>f</sub> of an element in its standard state?
Zero.
Define ΔH<sub>rxn</sub>.
The enthalpy change for a chemical reaction.
What is the effect of using the wrong state symbol (e.g., H<sub>2</sub>O(g) instead of H<sub>2</sub>O(l))?
It will lead to an incorrect ΔH<sub>rxn</sub> calculation.
What is the effect of not balancing the chemical equation correctly?
Incorrect stoichiometric coefficients will lead to an incorrect ΔH<sub>rxn</sub> 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.