The amount of beat released when 8.01 g of methanol are burned in the presence o

Question

The amount of beat released when 8.01 g of methanol are burned in the presence of a large excess of oxygen in a constant-pressure system (cylinder equipped with a movable piston) is: 11616 kJ -5815 kJ -363 kJ -181.5 kJ -90.75 kJ None of the above, the correct amount of heat is___J The enthalpies of formation of liquid hexane (C_6H_14), gaseous CO_2, and liquid water are -198.7 kJ, -393.5 kJ, and -285.8 kJ, respectively. The enthalpy reaction (deltaH) of the process; 2 C_6H_14(I) + 19 O_2(g) right arrow 12 CO_2(g) + 14 H_2O(l) is: -8326 kJ +4163 kJ +199 kJ +481 kJ +4163 kJ None of the above; the correct change in enthalpy is___J The number of orbitals in the n = 3 shell of an atom is: 3 4 6 9 12 16 18 32

Explanation / Answer

12)

we know that

moles = mass / molar mass

so

moles of CH3OH = 8.01 / 32 = 0.25

now

we can see that

2 moles of CH3OH ---> -1452 kJ

0.25 moles of CH3OH ---> y kJ

y = -1452 x 0.25 / 2

y = -181.5

so

amount of heat released is -181.5 kJ

so

the answer is d) -181.5 kJ

13)

consider the given reaction

2 C6H14 + 19 02 ---> 12 C02 + 14 H20

we know that

dHrxn = dHof products - dHof reactants

so

dHrxn = ( 12 x dHof C02 ) + (14 x dHof H20) - ( 2 x dHof C6H14) - ( 19 x dHof 02)

dHrxn = ( 12 x -393.5) + ( 14 x -285.8) - ( 2 x -198.7) - (19 x 0)

dHrxn = -8326 kJ

so

the change in enthalpy is -8326 kJ

so

the answer is option a) -8326 kJ

14)

we know that

number of orbitals = n2

so

number of orbitals = 3^2 = 9

so

option d) 9

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