[eleventhxhour]

1) A student placed 50.0mL of 2.05mol/L NaOH in a coffee-cup calorimeter at 20.4°C. After quickly stirring the mixture, its temperature rose to 28.2°C. Determine the enthalpy change for the reaction:

2NaOH(aq) + H2SO4(aq) --> 2H2O(l) + Na2SO4(aq)

I tried converting NaOH and H2SO4 into moles, and then finding the q=mcΔT of it, but you don't have the c of the compounds so I couldn't do that.

I also have another question:

2) Determine the energy released in the reaction of 1.00g of sodium with water.
2Na(s) + 2H2O(l) --> H2(g) + 2NaOH (aq) ΔH = -368.4kJ

So for this, I converted the sodium into moles. Then I plugged the moles and the combustion enthalpy into the equation ΔH=nΔHx to get 16.02kJ/mol. However, the answer says that it's 8.01kJ. What did I do wrong?

[Borek]

I tried converting NaOH and H2SO4 into moles, and then finding the q=mcΔT of it, but you don't have the c of the compounds so I couldn't do that.

Assume that of water. For relatively diluted solution that a reasonable approximation.

2) Determine the energy released in the reaction of 1.00g of sodium with water.
2Na(s) + 2H2O(l) --> H2(g) + 2NaOH (aq) ΔH = -368.4kJ

So for this, I converted the sodium into moles. Then I plugged the moles and the combustion enthalpy into the equation ΔH=nΔHx to get 16.02kJ/mol. However, the answer says that it's 8.01kJ. What did I do wrong?

You are wrong by exactly factor of two. 368.4 kJ per how many moles of Na(s)?

[eleventhxhour]

Assume that of water. For relatively diluted solution that a reasonable approximation.

I did this but I'm still getting the wrong answer. I converted both NaOH and H2SO4 from moles into grams and got 4.1g of NaOH and 5.88g of H2SO4. Then I used the equation qtotal = qNaOH + q H2SO4 with c as 4.18J/gC. This gave me 325J, which I wasn't sure what to do with. Would you plug that into the equation ΔH = nΔHx and solve for ΔHx? But what would you plug in for the moles? I tried using NaOH and H2SO4, and I got the answer wrong each time.

You are wrong by exactly factor of two. 368.4 kJ per how many moles of Na(s)?

2 moles of Na, right? That makes sense! Thanks (: [/quote]

[Borek]

Can't help you much without knowing the exact wording of the problem. You have not told us how much acid there was.

You don't need masses of substances, numbers of moles are enough.