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Offline HelpME

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I need some serious chemistry help.
« on: March 24, 2007, 11:17:41 PM »
Hey guys,

this is really my last resort, can anyone help me with my homework? I feel like Im reading chinese, its this damn e-grade crap.

1.Calculate the kinetic energy (in J) of a proton moving at a speed of 2360 m/s

2. A piece of silver whose mass is 19.8 g is immersed in 22.3 g of water. The system is heated electrically from 24.0 to 37.6oC.



How many joules of energy are absorbed by the silver?
J

How many joules of energy are absorbed by the water?
J

3. A stainless steel spoon weighs 21.0 g and is at a temperature of 18.5oC. It is immersed in 81.0 mL of hot coffee (T=84.0oC) in a Thermos flask. What is the final temperature of spoon + coffee? (Assume that the heat capacity of the spoon is the same as that of pure iron and that the heat capacity of the coffee is the same as that of pure water.)

4. A dish containing 124 g of water at 54.0oC is put in a refrigerator to cool. It is removed when its temperature is 5.50oC. What is q (in kJ) for the water?

5. When 10.00 mL of a solution of strong acid is mixed with 100.00 mL of a solution of weak base in a coffee-cup calorimeter, the temperature falls from 25.5oC to 22.5oC. Determine q for the acid-base reaction, assuming that the liquida have densities of 1.00 g/mL and the same heat capacities as pure water.

6. Determine ?Eoreaction for each of the following reactions. Report your answers to the nearest 0.1 kJ.



2NH3(g)+3O2(g)+2CH4(g)2HCN(g)+6H2O(g)
kJ

2Al(s)+3Cl2(g)2AlCl3(s)
kJ

formation of butanol
Cgraphite+H2(g)+O2(g) C4H9OH(l)




formation of sodium carbonate
Na(s)+Cgraphite+O2(g) Na2CO3(s)




formation of ozone
O2(g) O3(g)


7. Estimate the difference between ?Hreaction and ?Ereaction for the combustion of liquid butanol (C4H9OH) in excess O2, at T = 298 K.
J

8. It takes 93.0 J of heat to raise the temperature of 7.84 g of tin from 1.84oC to 56.6oC. What is
the molar heat capacity of tin?

9. Suppose 100.0 mL of 1.00 M HCl and 100.0 mL of 1.00 M NaOH, both initially at 25.0oC, are mixed in a Thermos flask. When the reaction is complete, the temperature is 31.8oC. Assume the solutions have the same heat capacity as pure water.
 
 
 Compute the heat released (in kJ).
  kJ

 Use your value to evaluate the molar heat of the neutralization reaction:

H3O+ + OH- 2H2O(l)

10.
 
 
 
 

If you can't help me do you know anyone that can, my homework is due tuesday at 11. I'm desperate.

Offline Yggdrasil

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Re: I need some serious chemistry help.
« Reply #1 on: March 25, 2007, 12:43:54 AM »
Please read the Forum Rules.  We are not here to do your homework for you.  If you want help with your problems, you are expected to have read your chem book first (you can find most of the answers by looking up simple equations in your textbook) and show that you've at least attempted to solve all of the problems first.

Offline HelpME

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Re: I need some serious chemistry help.
« Reply #2 on: March 25, 2007, 12:54:32 AM »
i have read the chapter at least twice, I understand the majority of it I am just having a lot of trouble with the problems. My teacher is not answering my e-mails, so again this is my last resort. And how and I suppose to prove to you that I have read the chapter in order to get help. Can someone at least give me their sn, so I can get walked through the problems.

Offline Yggdrasil

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Re: I need some serious chemistry help.
« Reply #3 on: March 25, 2007, 01:20:06 AM »
Some of these problems are really simple problems where you plug in numbers into equations (which should be in your book).

1.Calculate the kinetic energy (in J) of a proton moving at a speed of 2360 m/s

The equation for kinetic energy is (1/2)mv2.  You can find the mass of a proton in your book or on wikipedia (don't always trust wikipedia though).

Quote
2. A piece of silver whose mass is 19.8 g is immersed in 22.3 g of water. The system is heated electrically from 24.0 to 37.6oC.
How many joules of energy are absorbed by the silver?
How many joules of energy are absorbed by the water?

q = mc?T

Where q = heat, m = mass, c = specific heat, and ?T is the change in temperature.  You would need to look up the specific heats for water and silver.

Quote
3. A stainless steel spoon weighs 21.0 g and is at a temperature of 18.5oC. It is immersed in 81.0 mL of hot coffee (T=84.0oC) in a Thermos flask. What is the final temperature of spoon + coffee? (Assume that the heat capacity of the spoon is the same as that of pure iron and that the heat capacity of the coffee is the same as that of pure water.)

This is a little more difficult problem.  Here, you have water transferring heat to the spoon.  Because of conservation of energy, the heat lost by the water is equal to the heat gained by the spoon.

Quote
4. A dish containing 124 g of water at 54.0oC is put in a refrigerator to cool. It is removed when its temperature is 5.50oC. What is q (in kJ) for the water?

5. When 10.00 mL of a solution of strong acid is mixed with 100.00 mL of a solution of weak base in a coffee-cup calorimeter, the temperature falls from 25.5oC to 22.5oC. Determine q for the acid-base reaction, assuming that the liquida have densities of 1.00 g/mL and the same heat capacities as pure water.

Use the equations above.

Quote
6. Determine ?Eoreaction for each of the following reactions. Report your answers to the nearest 0.1 kJ.
2NH3(g)+3O2(g)+2CH4(g)2HCN(g)+6H2O(g)
2Al(s)+3Cl2(g)2AlCl3(s)
formation of butanol
Cgraphite+H2(g)+O2(g) C4H9OH(l)
formation of sodium carbonate
Na(s)+Cgraphite+O2(g) Na2CO3(s)
formation of ozone
O2(g) O3(g)

Look up Hess's law in your book.  To answer the question you would need to reference the table of standard free energies of formation in your book (probably an appendix).

This should be enough to get you started.

Offline HelpME

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Re: I need some serious chemistry help.
« Reply #4 on: March 25, 2007, 07:16:19 PM »
hey,

thanks so much for your help, the problem I was having with number was that I kept on using 1/2mv2 but my result keeps getting rejected.

This is what I exactly did and still am doing, in hope to get this answer correct.

1/2(1.67*10-27)(2360)2= 3.88E-20

I really apperciate your help.

Offline HelpME

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Re: I need some serious chemistry help.
« Reply #5 on: March 25, 2007, 07:53:25 PM »
sorry dude, I just now realized why I kept getting number 1 wrong. The questioned did so simple, but it was all about how I plugged in the numbers in the calulator. I squared the entire answer not the velocity by itself.

Offline HelpME

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Re: I need some serious chemistry help.
« Reply #6 on: March 25, 2007, 09:27:14 PM »
I am having some more questions regarding chemistry.

1. Using standard heats of formation, determine ?H for the following reactions. Report your answers to the nearest 0.1 kJ.
 
  Fe2O3(s) + 3H2O(l)2Fe(OH)3(s)
  kJ

B2O3(g) + 3H2O(l)2H3BO3(s)
  kJ
 
I am not sure how to approach this question.

2. Estimate the difference between ?Hreaction and ?Ereaction for the combustion of liquid butanol (C4H9OH) in excess O2, at T = 298 K.

I know I am have to use the enthalpy equation, but I am not coming out with the right answer.

3. A gold coin whose mass is 8.05 g is heated to 131.3oC and then quickly dropped into an ice calorimeter. What mass of ice melts? (The amount of heat in an ice calorimeter is determined from the quantity of ice the melts, knowing that it takes 6.01 kJ of heat to melt exactly one mole of ice.)

I am not sure if I have to use enthalpy equations or heat capacity equations.

4. What is the speed (in mile per hour) of a 50.7 kg runner whose kinetic energy is 484 J?

I am using the equation E=mv2/2, but I am not coming out with the right answer.

5. It takes 93.0 J of heat to raise the temperature of 7.84 g of tin from 1.84C to 56.6C. What is the molar heat capacity of tin?
 
I used this equation q= nC* change in tempreture, but I don't know if I have to find the number of moles in tin and what I am suppose to do with the 93.0 J of heat.

6. A home swimming pool contains 203 m3 of water. At the beginning of swimming season, the water must be heated from 20.0oC to 30.0oC.
 
 How much energy (in kJ) must be supplied?
  kJ


 If a natural gas heater supplies this energy with an 82.9 % heat transfer efficiency, how many grams of methane must be burned? (The heat of combustion of methane is -803 kJ/mol.)
  g
 
 I am using the molar heat capacity equation but I am still having trouble with it.

Thanks for your help, I really apperciate it. My teacher gives way too much homework that gives me a headache.
 

 

Offline Yggdrasil

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Re: I need some serious chemistry help.
« Reply #7 on: March 26, 2007, 04:38:44 PM »
1. Using standard heats of formation, determine ?H for the following reactions. Report your answers to the nearest 0.1 kJ.
Fe2O3(s) + 3H2O(l)2Fe(OH)3(s)
B2O3(g) + 3H2O(l)2H3BO3(s)
I am not sure how to approach this question.

This is just another Hess's law problem.  I'm sure your chemistry text has an explanation of Hess's law and some examples.  To solve the problem, you would need to look up the standard heats of formation for these compounds, which you would probably find in the appendix of your chemistry text.

Quote
2. Estimate the difference between ?Hreaction and ?Ereaction for the combustion of liquid butanol (C4H9OH) in excess O2, at T = 298 K.

I know I am have to use the enthalpy equation, but I am not coming out with the right answer.

Could you show your work?  If might be easier for us to spot an error if you show us.

Quote
3. A gold coin whose mass is 8.05 g is heated to 131.3oC and then quickly dropped into an ice calorimeter. What mass of ice melts? (The amount of heat in an ice calorimeter is determined from the quantity of ice the melts, knowing that it takes 6.01 kJ of heat to melt exactly one mole of ice.)

I am not sure if I have to use enthalpy equations or heat capacity equations.

Here the equation you know that the coin goes from 131.3oC to 0oC, so you can calculate the heat lost by the coin.  The heat lost by the coin is equal to the heat gained by the ice.  When the ice gains heat, it melts and you would calculate the quantity of ice that melts using the equation:

q = n?Hfus

where n is the number of moles of ice which melt, and ?Hfus is the "enthalpy of fusion" of ice, which means the amount of heat needed to melt one mole of ice.  More on this equation should be in your book.

Quote
4. What is the speed (in mile per hour) of a 50.7 kg runner whose kinetic energy is 484 J?

I am using the equation E=mv2/2, but I am not coming out with the right answer.

Can you show your work?  Are you sure that your units are correct?

Quote
5. It takes 93.0 J of heat to raise the temperature of 7.84 g of tin from 1.84C to 56.6C. What is the molar heat capacity of tin?
 
I used this equation q= nC* change in tempreture, but I don't know if I have to find the number of moles in tin and what I am suppose to do with the 93.0 J of heat.

For molar heat capacity, you want n to be the number of moles of tin.  The C you calculate should have units of J/(mol * oC)

Quote
6. A home swimming pool contains 203 m3 of water. At the beginning of swimming season, the water must be heated from 20.0oC to 30.0oC.
 
 How much energy (in kJ) must be supplied?
  kJ


 If a natural gas heater supplies this energy with an 82.9 % heat transfer efficiency, how many grams of methane must be burned? (The heat of combustion of methane is -803 kJ/mol.)
  g
 
 I am using the molar heat capacity equation but I am still having trouble with it.

What kind of trouble?

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