<li> Consider the reaction below. When a 45.00 gram sample of ethanol is burned with excess oxygen, about how much energy is released as heat?</li>
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<p>C2H5OH(l) + 3O2(g)—>2CO2(g) + 3H2O(l)
∆H = -1.40 X 10^3 kJ
(A) 0.995 kJ
(B) 5.1 X 10^2 kJ
(C) 1.40 X 10^3 kJ
(D) 2.80 X 10^3 kJ
(E) 5000 kJ</p>
<p>The answer is C. how?</p>
<p>You're given the change in enthalpy for the reaction (∆H = -1.40 X 10^3 kJ). Since 1.40 x 10^3 kJ of energy are given off by the reaction, 1.40 x 10^3 kJ of energy is released as heat.</p>
<p>the 45 gram sample is acually almost equal to 1 mole....and in the reaction they've mentioned that when 1 mole of ethanol combusts, 1.4 X 10^3 KJ is released........so, C is the right answer</p>
<p>∆H = -1.40 X 10^3 kJ is the amount of energy released PER MOLE of ethanol</p>
<p>Convert 45.00 grams of ethanol into X number of moles</p>
<p>Now you have the amount of heat released per mole + the number of moles</p>
<p>So - solve</p>
<p>All I did was restate what was already said in a different way</p>
<p>i concur with those above me.. (though i dont need to) =/</p>
<p>erm.. do they actually ask stuff less superficial than this??</p>
<p>i feel kinda screwed right about now.. 4 days from exam and i dont really know much =/</p>