Air Acetylene
thermochemistry anyone…?
i need help with some questions.
The complete combustion of acetylene, C2H2(g), produces 1300. kJ of energy per mole of acetylene consumed. How many grams of acetylene must be burned to produce enough heat to raise the temperature of 1.00 gal of water by 9.19 °C if the process is 87.1 % efficient? Assume the density of water is 1.00 g/cm3.
Consider a mixture of air and gasoline vapor in a cylinder with a piston. The original volume is 40. cm3. If the combustion of this mixture releases 920. J of energy, to what volume will the gases expand against a constant pressure of 660. torr if all the energy of combustion is converted into work to push back the piston?
I can help with the first one.
Step one is to find out how much energy you need to raise 1 gallon of water by 9.19 degrees.
1 gallon = 3785.4 mL (I googled that)
1 mL = 1cm3
so 1 gallon = 3785 cm3
85g of water. (1 cm3 = 1g)
To raise one gram of water one degree celsius, you use 4.18J (specific heat of water). So, to raise 3785g of water 9.19 degrees, we use:
3785g x 4.18 J/gC x 9.19 C = 145397.7 J = 145.4 kJ
OKAY. Next we need to know how much energy is produced if the process is only 87.1% efficient. Easy!
0.871 * 1300 kJ = 1132.3 kJ is produced per mole)
145.4 kJ is needed x ( 1 mol / 1132.3 kJ ) = 0.1284 mol
Now we convert that to grams
0.1284 mol x (26 g/mol) = 3.34 g of acetylene.
Do make sure to check for math mistakes and do these steps yourself. I’m using my computer calculator and I may have mistyped (it’s also important that you work through it so you learn). Good luck!
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