In a generic chemical reaction involving reactants A and B and products C and D, aA+bB→cC+dD, the standard enthalpy ΔH°rxn of the reaction is given by
ΔH°rxn=cΔH°f(C)+dΔH°f(D) -aΔH°f(A)-bΔH°f(B)
Notice that the stoichiometric coefficients, a, b, c, d, are an important part of this equation. This formula is often generalized as follows, where the first sum on the right-hand side of the equation is a sum over the products and the second sum is over the reactants:
ΔH°rxn=∑productsnΔH°f-∑reactantsmΔH°f
where m and n represent the appropriate stoichiometric coefficients for each substance.
Part A
What is ΔH°rxn for the following chemical reaction?
H2O(l)+CCl4(l)→COCl2(g)+2HCl(g)
You can use the following table of standard heats of formation (ΔH°f) to calculate the enthalpy of the given reaction.
|
Element/ Compound
|
Standard Heat of Formation (kJ/mol)
|
Element/ Compound
|
Standard Heat of Formation (kJ/mol)
|
|
H(g)
|
218
|
N(g)
|
473
|
|
H2(g)
|
0
|
O2(g)
|
0
|
|
CCl4(l)
|
-139.5
|
O(g)
|
249
|
|
H2O(l)
|
-285.8
|
HCl(g)
|
-92.30kJ
|
|
C(g)
|
71
|
COCl2(g)
|
-218.8kJ
|
|
C(s)
|
0
|
HNO3(aq)
|
-206.6
|
Express the standard enthalpy of reaction to three significant figures and include the appropriate units.