According to the given equation, how many moles of chlorine would be required to react completely with 1.0 moles of CH₄? Blank CH₄ plus blank CL₂ react to form blank CCL₄ plus blank HCL. A) 0.25 moles, B) 0.50 moles, C) 1.0 moles, D) 2.0 moles, or E) 4.0 moles.
Our job is to figure out the amount of chlorine that we need to react with one mole of CH₄. It’s important to recognise that chlorine here refers to CL₂, chlorine gas, and not chlorine atoms. The equation shows methane, CH₄, reacting with chlorine, CL₂, producing carbon tetrachloride and hydrogen chloride. The alternative name for HCL is hydrochloric acid although that’s more common when it’s in aqueous solution. This is an example of the halogenation of an alkane. Methane is the alkane. Chlorine is the halogen. And we see over the course of this reaction, each hydrogen on the methane being substituted with a chlorine atom.
Before we can rush in and say we use one mole of chlorine for each mole of methane, we have to check whether the equation is balanced. We have one carbon atom in our methane molecule and one carbon atom in our carbon tetrachloride molecule. So the carbon atoms are balanced. However, we have four hydrogens on the left and only one on the right. And the chlorine isn’t balanced either, with only two chlorines on the left, but five on the right.
Let’s pull away the names so we can see more clearly. The carbons are balanced. So if we increase the amount of methane, we’d also have to increase the amount of carbon tetrachloride. So we should try to avoid changing either of these numbers unless we have to. Now, let’s have a look at chlorine. Chlorine is present in one reactant and two products. This makes it a little tricky to balance because we have three numbers to change. And we don’t know exactly how to change them.
However, the other unbalanced element, hydrogen, is only in one reactant and one product. We want to keep the amount of methane the same. So let’s change the amount of hydrogen chloride. We want to increase the amount of hydrogen on the product’s side to four so that we balance out the amount on the reactant’s side. This brings the amount of hydrogen on both sides into balance. So hydrogen is balanced and we could move on to chlorine.
The reactants have less chlorine than the products. So we want to increase the amount of chlorine on the reactant’s side to eight to balance it out. We can do this by increasing the number of chlorine molecules on the left-hand side to four. The equation is now balanced in chlorine, hydrogen, and carbon. The balanced chemical equation tells us that we need four lots of chlorine per one lot of methane.
Therefore, the amount of chlorine we need to react completely with 1.0 moles of CH₄ is one mole of CH₄ multiplied by four moles of CL₂ per mole of CH₄. This works out as four times as many moles, which of course is 4.0 moles of CL₂.