For each of the reactions calculate the mass in grams of the...

For each of the reactions, calculate the mass (in grams) of the product that forms when 15.39 g of the underlined reactant completely reacts. Assume that there is more than enough of the other reactant. a. 2 K(s) + Cl2(g)-2 KCl(s) b. 2 K(s) + Br2(l)-2 KBr(s) c. 4 Cr(s) + 3 O2(g)-2 Cr2O3(s) d. 2 Sr(s) + O2(g)-2 SrO(s)

Transcript

00:01 So let's try to figure out how much product can be made with 15 .39 grams of one of our reactants.

00:09 So if we take a look at our first chemical reaction where we take potassium and chlorine and make potassium chloride.

00:27 If we start out with 15 .39 grams of our chlorine, how much casey, can we make? so the process in each of these is going to wind up being the same.

00:40 The first is we convert grams to moles that uses molar mass.

00:55 Then we're going to use the mole ratio that's based on the coefficients of our chemical reaction.

01:09 And then we have to convert back to grams and that's going to use molar mass.

01:19 Of our product.

01:24 Okay, so let's start out with our 15 .39 grams of cl2.

01:33 And now to convert to moles, we know that one mole of cl2 has a mass of 70 .906 grams.

01:44 How do i know that? when i go to the periodic table, i find that the mass of one of the cl2s is 35 .453.

01:53 I've got to the amount.

01:53 Two of them so i multiply that by two.

01:56 That gets us our moles of cl2 but we want to know about kcl so we use the mole ratio what we want to go to so we want to know about kcl the coefficient is two so for every two moles of kcl we want we use one mole of cl2 and then that final step is we have to get the molar mass of kcl so we'll look up the mass of k and about 39 point one, the cl 35 .453 will add them together and the molar mass is 74 .55 grams per mole.

02:42 And now if you take a look, grams of cl2 cancel out, moles of cl2 cancel out, moles of kcl cancel out.

02:51 So we're left with our grams of kcl.

02:53 We do our math to four significant figures and get 32 .36.

03:00 Grams.

03:02 That's how much product we're going to make.

03:05 And we can do that for several other chemical reactions.

03:10 So if we've got potassium, but instead of reacting with chlorine, we'll react it with bromine to make kbr.