# Chemistry

posted by molly

can you please please help me with these questions I don't know how to do any of them. I know how to calculate moles and grams and mole ratio,etc but I don't understand the limiting excess reactant and yield stuff. Thanks!

1.In the following chemical reaction, how many grams of the excess reactant are left over when 0.45 moles of Al react with 1.25 moles of Cl2 ?
2Al + 3Cl2 → 2AlCl3

2.Using the following equation, determine the % yield from the following reaction if 30.65 g of octane (C8H18 ) react with excess oxygen to produce 81.75 g of CO2

C8 H18 (I) + 25 O2 (g) → 16CO2 + 18H2O

moles of kcl=10.35/74.55=0.138

3.
For the following reaction, determine the amount of AgCl(s) formed when 10.35 g of KCl(aq) react with excess AgNO3 (aq) to produce AgCl(s) and KNO3 (aq) with a 77.15% yield.

AgNO3 + KCl → AgCl(s) + KNO3

1. DrBob222

1.In the following chemical reaction, how many grams of the excess reactant are left over when 0.45 moles of Al react with 1.25 moles of Cl2 ?
2Al + 3Cl2 → 2AlCl3

LR = limiting reagent. ER - excess reagent. Actually you work three regular stoichiometry problems here. First you want to identify the LR and ER and you do it this way.Use the coefficients in the balanced equation to convert mols Al AND mols Cl2 (in two separate operations) to mols AlCl3.
0.45 mols Al x (2 mols AlCl3/2 mols Al ) = 0.45 mols AlCl3 formed.

1.25 mols Cl2 x (2 mols AlCl3/3 mols Cl2) = 0.83 mols AlCl3.
IN LR problems the smaller number is ALWAYS the mols Product formed and the reagent responsible for that is the LR. In this case that makes Al the LR and Cl2 the ER.
Now that you know Cl2 is the ER, then you need to calculate the amount of Cl2 used. To do that just do the stoichiometry again; i.e., 0.45 mols Al x (3 mols Cl2/2 mols Al) = 0.68 mols Cl2 used.
1.25 mols Cl2 initially.
-0.68 mols Cl2 used
--------
1.25-0.68 = ? mols Cl2 not reacted.

2.Using the following equation, determine the % yield from the following reaction if 30.65 g of octane (C8H18 ) react with excess oxygen to produce 81.75 g of CO2

C8 H18 (I) + 25 O2 (g) → 16CO2 + 18H2O

moles of kcl=10.35/74.55=0.138
I don't know where this 0.138 mols KCl fit so I'll ignore it.

For problem #2, you say you know how to vind mols etc. Do this.
a. Convert grams octane to mols.
b. Use the coefficients in the balanced equation to convert mols octane to mols CO2.
c. Convert mols CO2 to grams CO2. THIS IS THE THEORETICAL YIELD (THE AMOUNT OF STUFF FORMED FOR 100% YIELD). I call this TY for theoretical yield. The actual yield (AY) is 81.75 g
d. %yield = (AY/TY)*100 = ?

3.
For the following reaction, determine the amount of AgCl(s) formed when 10.35 g of KCl(aq) react with excess AgNO3 (aq) to produce AgCl(s) and KNO3 (aq) with a 77.15% yield.

AgNO3 + KCl → AgCl(s) + KNO3

This looks like #2.

2. molly

thank you so much that makes so much sense :)

## Similar Questions

1. ### Chemistry

When 9.0g of Al were treated with an excess of chlorine, 20.0g of Al2Cl6 were collected. 2AL + 3Cl6 -------> Al2Cl6 What was the percentage yield?
2. ### chemistry

The first step of the synthesis is described by the reaction below. When 1.750 g of Fe(NH4)2(SO4)2 6H2O is mixed with 13 mL of 1.0 M H2C2O4 , the theoretical yield of FeC2O42H2O is ?
3. ### chemistry

for the reaction: 4NH3+5O2=4NO+6H2O; 15.0g of NH3 and 27.5g of O2 were reacted. a). which is the limiting reactant?
4. ### chemistry urgent

if 100 g of iron were reacted with 100 g of oxygen according to the reaction below, the maximum yield in grams of Fe2O3 would be: chemistry urgent - bobpursley, Tuesday, November 30, 2010 at 4:20pm Balance the equation. Note the coefficents …
5. ### chemistry

A gaseous mixture containing 5 moles of H2 and 7 moles of Br2 reacts to form HBr. Write a balanced chemical equation. Which reactant is limiting?
6. ### chemistry

Record and calculate the following masses: (a)mass of empty beaker: 47.420g (b)mass of beaker plus Na₂CO₃:47.920g (c)Mass of Na₂CO₃:0.5g (d)mass of beaker plus NaCl:47.438g (e) Mass of NaCl (g):0.018g **I need …
7. ### CHEMISTRY

A student combusted 0.500g of purified aluminum power with excess oxygen in an oxygen atmosphere according to the reaction, 4Al(s) + 3O2(g)= 2Al2O3(s) A) What is the limiting reactant?
8. ### Chemistry (Check and Help)

Upon the combustion of propane, C3H8, 150. g of propane was reacted with excess oxygen gas. A. Determine the limiting reactant if the water is the product of interest. B. Determine the number of grams of water produced. C. Calculate …
9. ### Chemistry

can you please please help me with these questions I don't know how to do any of them. I know how to calculate moles and grams and mole ratio,etc but I don't understand the limiting excess reactant and yield stuff. Thanks! 1.In the …
10. ### Chemistry

Calculations involving a limiting reactant Now consider a situation in which 20.0 g of P4 is added to 54.0 g of Cl2, and a chemical reaction occurs. To identify the limiting reactant, you will need to perform two separate calculations: …

More Similar Questions