[jamesbrown]

*Ignore me, I am impatient*

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

Thankyou

[Burner]

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*

Please read the forum rules. (http://www.chemicalforums.com/index.php?topic=65859.0). Don't bum p. Be patient.

[jamesbrown]

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?

[Borek]

What is mass of the solution?

Concentration is there just to let you find out the limiting reagent in the Mg/CuSO₄ reaction.

[jamesbrown]

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

[Burner]

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.

[jamesbrown]

So what is the mass then or could you tell me how to find it? I don't really get it

[jamesbrown]

Sorry is the mass 102 then? not 100.2 I was reading the wrong thing

[Burner]

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.

[jamesbrown]

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.

[Borek]

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?

[jamesbrown]

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

[Borek]

If you know volume, and density, can you calculate mass of the solution?

[jamesbrown]

Sorry thats all I was told about are you sure theres no way of doing this?

[Borek]

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.