How much heat is evolved upon the complete oxidation of 5 g of aluminum at 25 de

Question

How much heat is evolved upon the complete oxidation of 5 g of aluminum at 25 degree C and 1 atm pressure? Delta H^o_f for Al_2O_3 is - 1676 kJ/mol.) 4Al(s) + 3O_2(g) rightarrow 2Al_2O_3(s) 637.5 kJ 159.3 kJ 79.69 kJ 318.7 kJ 8.601 x 10^3 kJ the reaction of iron with hydrochloric acid is represented by the following thermochemical equation If. in a particular experiment, 3.66 kJ of heat was released at constant pressure, what volume of H_2(g), measured al STP, was produced? (R = 0 0821 L middot atm/(K middot mol)) 1 01 L 5.38 x 10^2L 5.88 x 10^2L 22 4 L 0.933 L

Explanation / Answer

35)

Ans- Option(b)

molecular wt of Al is 26.98 g/mol

hence no. of moles of aluminium reacted = 5/26.98 = 0.19 mol

For every aluminium reacted, theere is half aluminium oxide prodeuced.

hence aluminium oxide produced = 0.19/2 = 0.095 mol

heat of reaction = No. of moles of Al2O3 formed *  Hf

= 0.095 * 1676

= 159.22 kJ

36)

Ans- Option (d)

Let us assume the reaction of iron with hydrochloric acid produces 1 mol of H2 gas whcih produces -87.9 kJ energy.

Now at particular experiment, if 3.66 kJ heat is released at STP, then no. of moles of H2 gas produced = 3.66/87.9 = 0.0416 mols

Now by ideal gas law at STP,

P = 1 atm

T= 273 K

R = 0.0821 L-atm/K-mol

n = 0.0416

V = n*R*T/P

= 0.0416 * 0.0821 * 273 / 1

= 0.933 L

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