AP Chemistry

1) Calculate the volume of air at 30 degrees C and 1.00 atm that is needed to burn completely 10.0 grams of propane. Assume that air is 21.0 percent O2 by volume.

2) Assuming all of the heat evolved in burning 30.0 g of propane is transferred to 8.00 kg of water (specific heat = 4.18 j/goK), calculate the increase in temperature of the water.


One problem per post please.
1. Write the balanced equation.
C3H8 + 5O2 ==> 3CO2 + 4H2O

Convert 10g C3H8 to mols, use the equation to convert mols C3H8 to mols O2, and use that and PV=nRT to calculate volume at the non-standard conditions. That divided by 0.21 should be the volume of air. Check my thinking. Check my work.

2. Different problem but same equation. Are you given the delta H for the reaction? If it isn't given then you must look it up in a set of tables. Use the value in the tables (usually given in kJ/mol) to calculate deltaH for the reaction. Then q=increase in T.
q = mass x specific heat x deltaT. Delta T will be the increase in T.

Post your work if you get stuck.

To clarify, q is not the increase in T; rather, q is the heat transferred to the water; q = increase in heat and that is used to calculate T.

Okay, for 2 I got the delta H, which is -103.7 kJ/mol. So is the equation something like:

(.682 mol C3H8)(-103.7kJ/mol)=(800g)(4.18J/g-K)(delta T)

and I solve for Delta T?

Oh, nevermind I figured this out, thanks DrBob222 for the help!

asked by OhGodChemistry
  1. ahahhhaaaa.

    posted by zoozoo

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