Consider the combustion of hydrochloric acid. 4 HCl (aq) + O2(g) 2H2O(l) + 2 Cl2
ID: 929981 • Letter: C
Question
Consider the combustion of hydrochloric acid. 4 HCl (aq) + O2(g) 2H2O(l) + 2 Cl2(g) Hrxn = + 96.976 kJ/mol
B.If you place 750 mL of 0.500 M solution of HCl with 17.2 g of O2, will any oxygen remain? (Hint: limiting reagent problem)
C.What mass of chlorine gas (in grams) is produced?
D) How many molecules of Cl2 are produced based on part (B)
E) What mass of excess reagent remains after the limiting reagent is used up?
F) If the chemist collects 6.98 g of Cl2, what is the percent yield of the reaction? What is the percent error?
G) What is the enthalpy of the reaction for 24.5 g of HCl in presence of excess O2? Was energy absorbed or released into the surroundings?
Explanation / Answer
the reaction is
4 HCl + 02 ---> 2H20 + 2 Cl2
we know that
moles = molarity x volume (L)
so
moles of HCl = 0.5 x 0.75 = 0.375
also
moles = mass / molar mass
so
moles of 02 = 17.2 / 32 = 0.5375
now
4 HCl + 02 ---> 2H20 + 2 Cl2
moles of 02 required = ( 1/4) x moles of HCl
moles of 02 required = 0.25 x 0.375
moles of 02 required = 0.09375
but
0.5375 moles of 02 are present
so
02 is in excess , HCl is the limiting reagent
now
E)
moles of 02 left = 0.5375 - 0.09375 = 0.44375
mass of 02 left = 0.44375 x 32 = 14.2
so
14.2 grams of 02 is in excess
C)
now
4 HCl + 02 ---> 2H20 + 2 Cl2
moles of Cl2 formed = 0.5 x moles of HCl reacted
moles of Cl2 formed = 0.5 x 0.375
moles of Cl2 formed = 0.1875
mass of Cl2 fomred = 0.1875 x 71
mass of Cl2 produced = 13.3125 grams
D)
we know that
number of molecules = moles x avagadro number
so
number of Cl2 molecules = 0.1875 x 6.023 x 10^23
number of Cl2 molecules = 1.129 x 10^23
F)
% yield = actual x 100 / theoretical
% yield = 6.98 x 100 / 13.3125
% yield = 52.43
G)
now
moles = mass / molar mass
so
moles of HCl = 24.5 / 36.5
moles of HCl = 0.6712
now
4 moles of HCl ---> 96.976 kJ
0.6712 moles of HCl ---> y kJ
y = 0.6712 x 96.976 / 4
y = 16.273
so
16.273 kJ is the enthalpy
it has positive sign
so
energy is absorbed from the surroundings