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# Stoichiometry question for chemistry?

hey there, I'm in an online class and the course poorly explains stoichiometry, i was just wondering all the steps to finding the correct answer for.

What mass of lithium metal is needed to react with 8.35 L of nitrogen gas ?

it would be a great help, thanks!.

if possible add the steps i should take for questions like this. i just have a hard time in general trying to get the formula right.

really appreciate the help, it just bothers me that the teacher doesn't explain it like this in the first place. thanks a bunch, i understand how to do it now.

### 3 Answers

- KennyBLv 78 years agoFavorite Answer
1) You need the reaction. I'm going to assume that you make lithium nitride (this is not obvious from your question).

6Li + N2 --> 2Li3N

2) You do not give the temperature or pressure of the gas - so I am going to assume standard conditions (P = 1 atm, T = 273 degrees K). Now you can find the number of moles of N2 from the ideal gas law equation:

PV = nRT

to solve for n

n = PV/RT

where

P = 1 atm

V = 8.35 L

T = 273 K

R = 0.082 L-atm/deg-mol

this is about 0.37 moles (double check my math - I'm just using a SWAG)

Knowing n for N2, how many moles of Li do you need? Multiply by 6 (the stoichiometry) from the balanced equation) to find you need about 2.2 moles.

Finally, multiply by the atomic weight of Li to find the mass in grams. Report your answer to three significant figures. (I get about 13 but I'm terrible with a calculator.)

- FredLv 78 years ago
First balance the equation

6 Li + N2 = 2 Li3N

Since you did not give the pressure or temperature of the gas, I will assume it is at STP conditions.

where pressure is one atmosphere and temp is 0 degrees C or 273 Kelvin

Use the universal gas equation to solve for moles N2 gas

PV = nRT P = atmospheres pressure, V = volume in liters n = # moles gas

R= gas constant, .082 and T= Kelvin temp which is Celsius plus 273

solve for # moles n = PV over RT = (1 atm) (8.35 Liters) over (.082)(273 degrees K)

n = .373 moles N2 gas.

Use the balanced equation above as a math platform. Over the N2 enter .373 moles and below the N2 enter its coefficient of one mole

Now over the Li enter X moles and below the same enter its coefficient of 6 moles

Cross multiply through the equation and solve for X moles of Li I got 2.24 moles Li

Now change to grams. Grams Li = 2.24 moles Li times 7 grams per mole = 15.7 grams Li

Source(s): retired chem teacher USA - Anonymous5 years ago
A combination reaction is simply a reaction that combines two elements or compounds into a single product. Example: X + Y ---> XY ( X and Y can be elements or compounds) Anything that does not fit this category is not a combination reaction. Answer 4 is correct.