Chem Questions!

need help with these 5 and please try to show me how you did it as best as possible. thanks so much!

1.Phosphine (PH3) is made from the reaction of hydrogen gas and phosporus. If 120 grams of phosphorus are used how much hydrogen gas i neded for a complete reaction?

2. Consider the reaction of nitrogen gas with chlorine to form nitrogen trichloride. If 37.2 grams of nitrogen gas and 170.4 grams of chlorine are used, what is the yield of nitrogen trichloride?

3.When potassium chlorate is heated, potassium chloride and oxygen gas are formed. The percent yield of the reaction is 83.2%. How much potassium chlorate must be deomposed to produce 198.5 grams of oxygen?

4. A baloon filled with oxygen gas to a volume of 1.75L at 36 degrees celsius. The baloon is then heated to 72 degrees celsius. What is the volume of the heated baloon?

5.A sample of oxyen is collected over water at 22 degrees celsius and 752 mm Hg in a 125 mL flask. How many moles of dry (water vapor excluded) oxygen gas is collected?

 

You need to learn to write equations for each reaction first, then balance them. From these you can find the mole ratio and the grams to work out how much of each component to react.

1) 6H2 + P4 --> 4PH3

Ratio of phosphorus (P4) to hydrogen gas (h2) = 1:6 ie. 1 mol of p4 for every 6 moles of h2 gas

120 grams of phosphorous used. In moles = 120g/(123.89g/mol)
= 0.969 moles phosphorous in 120g
0.969 * 6 = 5.814 moles of H2 gas
= 5.814mol * 2.02g/mol = 11.744g of H2 gas needed

2) Make a balanced equation, do the same thing as above

3) Percentage yield as a decimal = 0.832
Your equation will be
2KClO3 --> 2KCl + 3O2
moles of oxygen produced in 198.5g = 198.5/3(32) = 2.078 mol (it's 3(32) because you have 3 moles of it in the equation above, and 32 is its molar mass)
So, overall decomposition:
x grams of KClO3 * 0.832 (% yield) must = 2.078 mol of oxygen
2(KClO3) = 245.1g/mol * 0.832 = 2.078mol (o2)
Therefore 612.26g of KClO3 are required

Bit iffy about that question myself, have to have a proper think about it, but that's the general idea that came to mind. Have a feeling I screwed up somewhere.

4) Is just p1v1=p2v2 sub in as necessary

5) pv = nRT
convert 752mm Hg into atm = 0.989 atm
And you have 125ml = 0.125L
R = universal gas constant, it's about 8.314 joules/mol Kelvin
Finally, T = temperature in Kelvin.. 22 degrees C + 273.15 = 295.15 K
Therefore, 0.989 x 0.125 = n x 8.314 x 295.15
n = 0.00005 mol
= 5*10^-5 moles oxygen gas

Look, it's best to not just copy my answers blindly. If you are planning to do any science degree at a university level, you will need to understand basic concepts like these. Just keep practicing, read through them slowly until you understand them. They were my worst part in high school as well, but through persistence and lots of practice I finally understood them. University chemistry gets far more difficult than simple stuff like this, so you're better off mastering it sooner rather than later.

 

Beat me to it :/
Was looking forward to this haha

 

Haha I just finished my last exam for the year yesterday so I was like hmm already bored feel like helping some people out
Plus chemistry is the one subject that has brought me so much pain and so much knowledge at the same time, that its just fun to help other people understand it better