Question

GAS QUESTION: 75 ml F reacts with 15 ml Cl2 to produce 30 ml ClF (2F+CL2=2ClF). Determine formula of ClF. answer=ClF5. How?

Answer 1

You need to fix your equation. First, fluorine and chlorine are both diatomic gases under standard conditions (which is what we're assuming here), so we're working with F2 and Cl2. Second, how do you know what the coefficients in the equation are if you don't know the identity of the product? That's what we're trying to find out. Before doing anything, all we can say for sure is:

\[?? \space F_2\space + \space ?? \space Cl_2 \space \rightarrow \space ?? \space Cl_xF_y\]
Where x is the number of Cl atoms in the product and y is the number of F atoms in the product.

Since temperature and pressure aren't changing (I'm assuming), we can use volume as an indirect way to measure how much of each reactant and product there are, at least relative to each other. We have 75 mL of F2, 15 mL of Cl2, and 30 mL of Cl(x)F(y). Compared to Cl2, there is 5 times as much volume of F2, meaning there are also 5 times as many moles of F2 (5 times the moles occupy 5 times the space at the same temperature and pressure). Similarly, compared to Cl2, there is twice as much volume of Cl(x)F(y), meaning there are also twice as many moles of Cl(x)F(y) (2 times the moles occupy 2 times the space at the same temperature and pressure). That means we can update our chemical equation as follows:

\[5F_2\space + \space Cl_2 \space \rightarrow \space 2Cl_xF_y\]
Since this is a synthesis reaction, all reactants go into forming a single product. This means that if there are 5 F2 = 10 F atoms on the left, there also needs to be 10 F atoms on the right. For the equation to balance properly, y must equal 5. Similarly, if there is 1 Cl2 = 2 Cl atoms on the left, there also needs to be 2 Cl atoms on the right. For the equation to balance properly, x must equal 1. That means your final equation is:

\[5F_2\space + \space Cl_2 \space \rightarrow \space 2ClF_5\]
And the identity of your unknown product is ClF5! Hope that made sense, but if you have any questions let me know!