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### missed question test 1

Posted: Mon Nov 04, 2019 10:25 pm
Silicon nitride Si3N4, a material used for spinal fusion devices is made by reacting Si and Nitrogen gas (N2) at high temperatures. How much Si (in grams) is needed to react with an excess of N2 to prepare 120g of Si3N4 if the precent yield for the reaction is 100%.

Can someone show their calculations on what they did for this problem. I have trouble calculating percent yield.
All I know is that you are suppose to balance the chemical equation before study and find the molar mass of Si3N4.

### Re: missed question test 1

Posted: Mon Nov 04, 2019 10:32 pm
Take the given value of grams, divide by the molar mass. Now you have Si3N4 in moles. Use the molar ratio from the balanced equation to multiply by moles of Si. Now you have Si in moles. Multiply by the molar mass of Si. Now you have Si in grams, your answer. The process is dimensional analysis, using equivalent ratios to find an unknown quantity.

### Re: missed question test 1

Posted: Tue Nov 05, 2019 12:09 am
Just some extra information for this type of question, if they give you a percent yield that isn't 100%, you have to use the formula % yield = actual/theoretical to find the theoretical as the starting value of grams. Then, you'd follow the process that was explained above.

For example:
50g of Si3N4 if the precent yield for the reaction is 86%

actual = 50 g
% yield = 0.86
theo. = ?

0.86 = 50/theo.
theo = 58.1g

Then you would use 58.1g Si3N4 to then convert to moles, then use the ratio from the balanced equation to convert to Si moles, and multiply by the mass of Si. And that would be your answer.

### Re: missed question test 1

Posted: Thu Dec 05, 2019 7:20 pm
thanks!

### Re: missed question test 1

Posted: Thu Dec 05, 2019 8:17 pm
convert the g/mol mass to moles and multiply that by the molar ratio and then multiply by the g/mol mass of Si to get grams of Si