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**Here is the example I was given:**

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Example:

How many liters of hydrogen gas can be produced at 290 K and 2.5 atm if 40.0 g of sodium react with excess water according to the following equations:

2 Na(s) + 2 H2O(l) --> 2 NaOH(l) + H2(g)?

1. Write down the quantities you know.

T - 290 K

P = 2.5 atm

n = find from sodium and balanced equation.

R = 0.821 L atm/K mol

V = ?

2. Set up the problem.

First find how many moles of hydrogen can be produced from the 40.0 g of sodium (equation).

http://osd.flvs.net/webdav/educator_chemistry_v5/module6/imagmod6/6_14_a.gif

Now use PV = nRT to solve.

(2.5 atm)V = (0.870 mol) (0.0821 L atm)/K mol) (290K)

V = 8.3 L

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**And here are the questions I am having SO much trouble solving. Please help me out with these!**

1) C3H8(l) + 5O2(g) ---> 3CO2(g) + 4H2(g)O(g)

In the combustion of 250 g of propane with an excess of hydrogen, what volume of carbon dioxide is produced at 290 K and 1.5 atm. Choose from the following possible answers:

11904.5 L

270 L

90 L

404 L

2) Magnesium burns in oxygen gas to produce magnesium oxide. What mass of magnesium will react with a 0.25 L container of oxygen gas at 80oC and 770 mmHg?

.209 g

.945 g

.418 g

.124 g

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**It helps that they are multiple choice, but the example doesn't help me much. I don't understand how to solve these. :grumpy:**

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