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

Question

How much heat is evolved upon de complete oxidation of 5 g of aluminum at 25 degree C and v atm pressure? Delta H degree _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 times 10^3 kJ The reaction of iron with hydrochloride acid is represented by the following thermochemical equation. Fe(s) + 2HCl(aq) rightarrow FeCl_2(aq) + H_2(g); delta H degree = -87.9 kJ If, in a particular experiment, 3.66 kJ of heat was released at constant pressure, what volume of H_2O a measured at STP, was produced? (R = 0.0821 L. atm/k mol) 1.01 L 5.38 times 10^2 L 5.88 times 10^2 L 22.4 L 0.933 L Two metals of equal mass with different heat capacities are subjected to the same amount of the undergoes the smaller change in temperature? You need to know which metals you have. The metal with the higher heat capacity undergoes the smaller change in temperature. You need to know the initial temperatures of the metals. d. Both undergo the same change in temperature. The metal with the lower heat capacity undergoes the smaller change in temperature. Exactly 209.1 J will raise the temperature of 10.0 g of a metal from 25.0 degree C to 60.0 degree C. What heat capacity of the metal? 14.7 J/g degree C) 0.597 J/g degree C) 1.67 J/(g degree C) 50.0 J/(g degree C) none of these

Explanation / Answer

1) 5 g of aluminium is reacting hence 5/MW = 5/ 26.98 = 0.185 moles of Al has to be oxidsed

when 4 moles of Al will give 2 moles Al2O3

0.185 moles of Al will give 0.0925moles of Al2O3

given heat evolved for one mole of Al2O3 is 1676 kJ/mol

heat for 0.0925 moles of Al2O3 is 0.0925*1676 =159.3 kJ   Answer (b)

2)

87.9 kJ of heat is released for one mole of H2

3.66kJ of heat is released for 3.66/87.9 = 0.0416 mole of H2

PV = nRT

V = nRT/ P STP means P = 1 atm T = 273.15 K and R = 0.08206 L.atm/mol.K

= 0.0416 * 0.08206 * 273.15/ 1

V = 0.933 L answer ( e)

3)

( b) Metal with higher heat capacity will undergo smaller heat change answer

H = m Cp (T2 - T1)

Cp inversely proportional to temperature change

4)

H = m Cp (T2 - T1)

209.1 = 10*Cp * (60-25)

Cp = 0.597 J/g 0C   Answer

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