General Chemistry Principles, Patterns, and Applications, 2011

Answer:
a. 2C(s) + O 2(g) + 2H 2(g) → CH 3CO 2H(l)
Standard Enthalpies of Reaction
Tabulated values of standard enthalpies of formation can be used to calculate enthalpy changes
for any reaction involving substances whose values are known.
Thestandard enthalpy of reaction (ΔHrxnο) is the enthalpy change that occurs when a
reaction is carried out with all reactants and products in their standard states. Consider the general reaction
Equation 5.25
aA + bB → cC + dD
where A, B, C, and D are chemical substances and a, b, c, and d are their stoichiometric coefficients. The magnitude
of DHorxn is the sum of the standard enthalpies of formation of the products, each multiplied by its appropriate
coefficient, minus the sum of the standard enthalpies of formation of the reactants, also multiplied by their
coefficients:
Equation 5.26
DHorxn = [cDHo f C
More generally, we can write
Equation 5.27
( ) + dDHo f D
DHorxn = SmDHo f products
( )]products -[aDHo f A
( ) - SnDHo f ( reactants)
( ) + bDHo f B
( )]reactants
where the symbol Σ means “sum of” and m and n are the stoichiometric coefficients of each of the products and the
reactants, respectively. “Products minus reactants” summations such as arise from the fact that enthalpy is a state
function. Because many other thermochemical quantities are also state functions, “products minus reactants”
summations are very common in chemistry; we will encounter many others in subsequent chapters.
Note the Pattern
“Products minus reactants” summations are typical of state functions.
To demonstrate the use of tabulated values, we will use them to calculate for the combustion of glucose, the reaction
that provides energy for your brain:
Equation 5.28
C 6 H 12 O 6 (s) + 6O 2 (g) → 6CO 2 (g) + 6H 2 O(l)
Saylor URL: http://www.saylor.org/books
Saylor.org
439