How to determine the heat evolved or consumed by the reaction of 1.0 g SO2(g) with excess oxygen, with results from a Hess' Law Equation?

Question

Peyton Adams · Accepted Answer

(A)  Hess's Law asserts that you can: based on the enthalpy's state function property Additionally, you can maintain the validity of your response by adhering to these two procedures. The responses at your disposal are: (1) #2"S"(s) + 3"O"_2(g) -> 2"SO"_3(g)#, #Delta"H"_1 = -"790 kJ/mol"#
(2) #"S"(s) + "O"_2(g) -> "SO"_2(g)#, #Delta"H"_2 = -"297 kJ/mol"# to accomplish: (3) #2"SO"_2(g) + "O"_2(g) -> 2"SO"_3(g)#, #Delta"H"_"rxn" = ???# Since these responses are in fact error-free at startup, let's continue. Consequently, your last actions become: #cancel(2"S"(s)) + 3"O"_2(g) -> 2"SO"_3(g)#
#2("SO"_2(g) -> cancel("S"(s)) + "O"_2(g))#
#"--------------------------------------"#
#color(blue)(2"SO"_2(g) + "O"_2(g) -> 2"SO"_3(g))# Persuade yourself that the oxygen and sulfur are in balance! You can now calculate the enthalpy by doing the following: #color(blue)(Delta"H"_"rxn") = Delta"H"_1 + (-2)Delta"H"_2# #= -790 + (-2)(-297) "kJ/mol"# #=# #color(blue)(-"196 kJ/mol")# Also, be sure to clarify whether it's a standard reaction (i.e. the pressure according to STP, and #25^@ "C"#) or not. I think you were missing that, because there is no specified temperature in this question. (B) In this part, in knowing that you use "excess oxygen", you assume that #"SO"_2(g)# is the limiting reagent (i.e. it is entirely consumed first, and the reaction ends after that point), and from there, utilize the following equation for heat flow at a constant pressure: #\mathbf(Delta"H"_"rxn" = (q_"rxn")/"mols limiting reagent" = (q_"rxn")/(n_("SO"_2(g))))# I'm assuming that parts (A) and (B) have the same reaction conditions, that is, the same temperature and pressure. Consequently, the heat flow involved in this reaction should be as follows: #color(blue)(q_"rxn") = n_("SO"_2(g))Delta"H"_"rxn"# #= stackrel(n_("SO"_2(g)))overbrace((1.0 cancel("g SO"_2))((cancel("1 mol SO"_2))/(64.063 cancel("g SO"_2))))stackrel(Delta"H"_"rxn")overbrace((-"196 kJ/"cancel"mol"))# #= color(blue)(-"3.06 kJ")# You can choose the wording for your response because heat is produced by the reaction and exits the reaction because the sign of the heat flow is negative.

Natalie Anton · Answer

undefined To determine the heat evolved or consumed by the reaction of 1.0 g SO2(g) with excess oxygen using Hess' Law Equation, follow these steps:

1. Write the balanced chemical equation for the reaction.
2. Calculate the enthalpy change for each individual reaction involved in the process.
3. Use Hess' Law Equation to find the overall enthalpy change for the reaction by summing the enthalpy changes of the individual reactions, taking into account their stoichiometric coefficients.
4. Convert the given mass of SO2(g) to moles.
5. Use the molar enthalpy change obtained from Hess' Law to calculate the heat evolved or consumed for the given amount of SO2(g).