October 02, 2023, 03:14:09 PM
Forum Rules: Read This Before Posting

### Topic: General Energy Calculations  (Read 24875 times)

0 Members and 1 Guest are viewing this topic.

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #15 on: April 05, 2016, 07:33:39 PM »
*Ignore me, I am impatient*

Could someone please check this for me as I think its wrong.

Thankyou
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Burner

• Full Member
• Posts: 198
• Mole Snacks: +15/-2
• Gender:
• Chem-is-try
##### Re: General Energy Calculations
« Reply #16 on: April 05, 2016, 08:51:26 PM »
then for question 3 it says calculate the moles of fuel burned:
which is 0.4/58
moles = 0.0069
I think

then question 4 says calculate the heat released in KJ/mol of fuel burned
so for that would it be 22.76/0.0069 or is that wrong?

Correct.

*Ignore me, I am impatient*

Year 1 science student in HKUST and a Chemistry geek.
If I make any mistakes in the forum, please don't hesitate to correct me as I want to learn.

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #17 on: April 06, 2016, 07:22:04 AM »
Thanks you!

Also another thing say If the specific heat capacity of water is 4.2 J/g/°C and the mass of 1cm3 of water is 1g

then 100cm3  of 0.20 mol/dm3 copper sulphate solution was put in a calorimeter and 2.0g of magnesium power added. The temperature of the solution rose by 25.1 °C.

Calculate the heat released in KJ.

So would you do q = m*Δt*c

q = 0.2*25.1*0.0042
q = 0.021KJ

Is this right because the concentration part is confusing me?
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Borek

• Mr. pH
• Deity Member
• Posts: 27424
• Mole Snacks: +1783/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: General Energy Calculations
« Reply #18 on: April 06, 2016, 07:46:58 AM »
What is mass of the solution?

Concentration is there just to let you find out the limiting reagent in the Mg/CuSO4 reaction.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #19 on: April 06, 2016, 07:55:42 AM »
Do I have to add an extra 100g to the mass because 1cm3 is 1g and it state sthere is 100cm3

So the calculation would be 100.2*25.1*0.0042

Is this right, I'm kind of stuck at he moment due to our teacher not giving us usable notes
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Burner

• Full Member
• Posts: 198
• Mole Snacks: +15/-2
• Gender:
• Chem-is-try
##### Re: General Energy Calculations
« Reply #20 on: April 06, 2016, 07:59:28 AM »
Do I have to add an extra 100g to the mass because 1cm3 is 1g and it state sthere is 100cm3

So the calculation would be 100.2*25.1*0.0042

Is this right, I'm kind of stuck at he moment due to our teacher not giving us usable notes

For the equation Q=mcΔT

The m refers to the mass, but not molarity or concentration, of the substance.

Your 100.2 seems to come from 100g of solution + 0.2 mol dm-3 of solution, which is not correct.
Year 1 science student in HKUST and a Chemistry geek.
If I make any mistakes in the forum, please don't hesitate to correct me as I want to learn.

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #21 on: April 06, 2016, 08:21:43 AM »
So what is the mass then or could you tell me how to find it? I don't really get it
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #22 on: April 06, 2016, 08:22:52 AM »
Sorry is the mass 102 then? not 100.2 I was reading the wrong thing
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Burner

• Full Member
• Posts: 198
• Mole Snacks: +15/-2
• Gender:
• Chem-is-try
##### Re: General Energy Calculations
« Reply #23 on: April 06, 2016, 08:45:46 AM »
Sorry, but I start getting a little confused.

then 100cm3  of 0.20 mol/dm3 copper sulphate solution was put in a calorimeter and 2.0g of magnesium power added. The temperature of the solution rose by 25.1 °C.

Number of moles of magnesium= 2/24.3 = 0.0823 mol
Number of moles of copper sulphate= 0.1*0.2= 0.02 mol

Magnesium is in excess. Not all magnesium will be dissolved. Also, some copper metal is formed too. Calculating the mass in this case can be complex, is it (100g + mass of magnesium unreacted + mass of copper formed)? Please someone answer this.
Year 1 science student in HKUST and a Chemistry geek.
If I make any mistakes in the forum, please don't hesitate to correct me as I want to learn.

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #24 on: April 06, 2016, 09:11:39 AM »
Exactly, its hard for people like you and I just started being taught it like a week ago. So I think you can see where I am coming from and why I need help.
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Borek

• Mr. pH
• Deity Member
• Posts: 27424
• Mole Snacks: +1783/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: General Energy Calculations
« Reply #25 on: April 06, 2016, 02:16:18 PM »
You have 100 mL of solution. Let's assume its density is that of water (they differ a bit, but the difference is not large). Do you remember what is the density of water? If you know volume, and density, can you calculate mass of the solution?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #26 on: April 06, 2016, 02:37:49 PM »
All I know is the specific heat capacity of water is 4.2 J/g/°C and the mass of 1cm3 of water is 1g

100cm3  of 0.20 mol/dm3 copper sulphate solution was put in a calorimeter and 2.0g of magnesium power added. The temperature of the solution rose by 25.1 °C.

And I was told to calculate the heat released in the reaction in KJ
« Last Edit: April 06, 2016, 03:33:08 PM by jamesbrown »
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Borek

• Mr. pH
• Deity Member
• Posts: 27424
• Mole Snacks: +1783/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: General Energy Calculations
« Reply #27 on: April 06, 2016, 03:42:20 PM »
If you know volume, and density, can you calculate mass of the solution?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### jamesbrown

• Regular Member
• Posts: 55
• Mole Snacks: +1/-8
##### Re: General Energy Calculations
« Reply #28 on: April 06, 2016, 04:48:43 PM »
Sorry thats all I was told about are you sure theres no way of doing this?
Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

#### Borek

• Mr. pH
• Deity Member
• Posts: 27424
• Mole Snacks: +1783/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: General Energy Calculations
« Reply #29 on: April 06, 2016, 05:00:59 PM »
There is a very simple way of calculating mas of the solution, which comes directly from the density definition. You are expected to know such things.

Please note that you should never think in terms of a "it is not a part of what we have learned yesterday". Every piece of everything you have learned in the past matters.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info