Answer 4.3.1: Writing a balanced reaction

Problem:

The reaction between propane and hydrogen chloride to form propyl chloride and hydrogen is carried out in a continuous reactor. The product stream is analyzed and found to contain 27.45 mole% C3H7Cl, 27.45 mole % H2 and 14.6% HCl. The feed to the reactor contains only propylene and hydrogen chloride. Calculate the fractional conversion of the limiting reactant and the percentage by which the other reactant is in excess. If the molar flow rate of the feed stream is 209 mol/s, what is the extent of reaction? (Give its numerical value and its units.)

Explanation:

Let's ask ourselves a few questions:

What are our reactant species?

We're told that only propane (C3H8) and HCl are entering the reactant so these have to be our two reactants. We can then write:

C3H8 + HCl -> ???


What are our products?

We know we're getting propyl chloride (C3H7Cl) out, so we can now write:

C3H8 + HCl -> C3H7Cl + ???


And if we count up all the atoms we see that we have 2 H's on the left that aren't on the right yet. Those two atoms of hydrogen left over from the reaction will combine to give us H2 and the final balanced equation is:

C3H8 + HCl -> C3H7Cl + H2

You should write down the following number on a piece of paper because you'll need it when you're done figuring out all the steps that can be done on the other web page:

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