1. A reaction that is used to propel rockets is N 2 O 4 (l) + 2N 2 H 4 (l) --> 3

Question

1. A reaction that is used to propel rockets is N2O4(l) + 2N2H4(l) --> 3N2(g) + 4H2O(g). This reaction has the advantage that neither product is toxic, so no dangerous pollution is released. When the reaction consumes 10.0 g of liquid N2O4, it releases 124 kJ of heat. What is the value of %u0394H (in kJ per mole N2O4) for the chemical equation as written?

2. Ammonia is produced commercially by the direct reaction of the elements. The formation of 1.00 moles of gaseous NH3 by this reaction releases 46.17 kJ of heat. How much energy (in kJ) is released, when 67.0 kg of hydrogen gas, H2, reacts in excess nitrogen gas, N2?

3. The thermochemical equation for the burning of ethyl alcohol is

C2H5OH(l) + 3O2(g) --> 2CO2(g) + 3H2O(l)    %u0394H = -1,367 kJ

What is the enthalpy change (in kJ) for burning 14.93 g of ethyl alcohol?

Explanation / Answer

1)1 mole of N2O4 has mass of 92.01 so in 10 g we have 10 / 92.01 moles = 0.109 moles

these produce 124 kJ of heat so 1 mole will release 124 / .109 kJ / mole = 1138 kJ / mole

2)moles H2 = 67000 g/ 2 g/mol= 33500

n2 + 3 H2 = 2 NH3
moles NH3 = 33500 x 2/3=22333.33

Q = 22333.33 mol x 46.17 kJ= 1031130 kJ

3)For 1 mole of C2H5OH the enthalpy change = -1,367 kJ

I mole of C2H5OH = 46.07 g

So burning 14.93 g C2H5OH will produce an enthalpy change = -1,367 kJ x 18.05g / 46.07g = -443.006KJ

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