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### Topic: Can Someone Walk Me through these Stoichiometry Problems?  (Read 6048 times)

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#### Brndnjng

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##### Can Someone Walk Me through these Stoichiometry Problems?
« on: June 04, 2006, 09:49:46 PM »
Hey can someone walk me through these stochiometry problems step-by step? Parts of the concept is confusing me and I needed some examples to go by. Thanks in advance.

In the following sythesis reaction how many liters of ammonia at STP, are needed to fully react with 30.mL of 2.1M H2SO4 according to the equation:
2H3+H2SO4=(NH4)2SO4

#### anarchron

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #1 on: June 04, 2006, 10:00:06 PM »
Hey can someone walk me through these stochiometry problems step-by step? Parts of the concept is confusing me and I needed some examples to go by. Thanks in advance.

In the following sythesis reaction how many liters of ammonia at STP, are needed to fully react with 30.mL of 2.1M H2SO4 according to the equation:
2H3+H2SO4=(NH4)2SO4

Typo

The equation should look like this

2NH3(g) + H2SO4(aq) -> (NH4)2SO4(aq)

Firstly calculate n(H2SO4) = 0.03 * 2.1 = 0.063mol

From the equation, the reaction is a 2:1 reaction, hence

n(NH3) = 0.064 * 2 = 0.126

From there on you can choose to either use PV=nRT or Molar Gas Volume. Personally would choose Molar Gas Volume. Therefore

v(NH3) = 22.4 * 0.126 = 2.8 L

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#### Brndnjng

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #2 on: June 04, 2006, 10:37:46 PM »
Ok thanks.

This is the other one that's troubling me:

For the single replacement reaction of chlorine with potassium bromide, 300g of potassium bromide is combined with excess chlorince. 20L of bromine is collected at 45 degrees C and 1.2 atm. What is the percent yield of this reaction?

#### Dan

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #3 on: June 05, 2006, 03:30:09 AM »
1. Write a balanced equation.
2. How many moles of KBr do you have? (300g)
3. What is the maximum number of moles of Br2 that could possibly be produced by this many moles of KBr?
4. How many moles of Br2 are actually produced? (20L at 45degC, 1.2 atm)
5. Percent yield = (amount of product produced/max possible amount of product that could be produced)x100

ie. %yield = (answer 3 / answer 5)x100
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#### AWK

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #4 on: June 05, 2006, 05:36:09 AM »
Ok thanks.

This is the other one that's troubling me:

For the single replacement reaction of chlorine with potassium bromide, 300g of potassium bromide is combined with excess chlorince. 20L of bromine is collected at 45 degrees C and 1.2 atm. What is the percent yield of this reaction?
At this condition bromine is a liquid. Volume of bromine will be about 70 cm3. With excess of chlorine Br2 reacts to form BrCl.
AWK

#### Donaldson Tan

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #5 on: June 06, 2006, 02:47:52 PM »
At this condition bromine is a liquid. Volume of bromine will be about 70 cm3. With excess of chlorine Br2 reacts to form BrCl.

We can simplify the problem by ignoring the formation of BrCl.

AWK is right to point out the Br2 is a liquid at the given condition, so the density of the Bromine must be used to evaluate its molar quantity.
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#### Borek

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##### Re: Can Someone Walk Me through these Stoichiometry Problems?
« Reply #6 on: June 06, 2006, 03:13:52 PM »
Liquid bromium density - 3.2 g/mL.

That gives about 31800% yield
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