# 1.05 g MgO is added to 110.15ml HCL with an initial temperature

1. Feb 14, 2010

### haber101

1.05 g MgO is added to 110.15ml HCL with an initial temperature of 21.5 degrees Celsius and a final temperature of 34.5 degrees Celsius. calculate the KJ of energy released for the reaction. assume that 4.18 J of energy is required to change the temperature of one mL of solution to one Celsius degree.

my thinking. q=mcdeltat

q=?
m=110.15ml
c=4.18kj
delta t=13

=(110.15)(4.18)(13)
=5985.55Kj
=6.0x10^3

Last edited: Feb 14, 2010
2. Feb 15, 2010

### Staff: Mentor

Re: reaction

Your thinking is not incorrect, but you are incredibly cruel to your units. Mass is not in ml, and your use of k is completely off.

Last edited by a moderator: Aug 13, 2013
3. Feb 15, 2010

### haber101

Re: reaction

thanks, so how about i transfer the 110.15ml to grams which is 110.15g and then do q=mc$$\delta$$t
q=(110.15g)(4.18J/g^oC)(13^oC)
q=5985.551 J = 598 KJ
q=5.9x10^3 J

so the answer is q= 598 KJ or q=5.985x10^3 J ??

better?

also how can I calculate KJ/mol of MgO from this? has to do with the molar mass in guessing? which for Mg is 24.31 and oxygen 16.0 so 40.31 so 5985/40.31=148.47 Kj/mol of MgO. did i do this correctly?

Last edited by a moderator: Aug 13, 2013
4. Feb 15, 2010

### Staff: Mentor

Re: reaction

Very nice and very correct.

Nice try - but wrong. kJ is 1000 Joules.

No. You need molar mass, but you have to use it to calculate number of moles of MgO. Again - if you would pay attention to units it would be obvious something is wrong.

Last edited by a moderator: Aug 13, 2013
5. Feb 15, 2010

### haber101

Re: reaction

ok, thanks, i see so it must be 5.98KJ, makes sense

for the second part, hmmm how about if i did the amount of MgO which is given

(1.05g MgO)(1mol MgO)/(40.31 g MgO)=.0260

Last edited by a moderator: Aug 13, 2013
6. Feb 15, 2010

### Staff: Mentor

Re: reaction

As usual you omitted units in your answer, but I guess you mean 0.0260 moles of MgO?

You know 5.98 kJ (beware: small k, not capital K) was produced by reaction of 0.0260 moles of MgO. Now just combine these numbers so that the answer is in kJ/mol.

Last edited by a moderator: Aug 13, 2013
7. Feb 15, 2010

### haber101

Re: reaction

yes that is what i meant, my apologies

by combine do you just mean say that there is 5.98 kJ per 0.0260 moles of MgO

or 5.98kJ/0.0260 mol MgO= 230kJ/mol

Last edited by a moderator: Aug 13, 2013
8. Feb 15, 2010

### Staff: Mentor

Re: reaction

Looks OK

Note: I have not checked numbers, but they look reasonable.

Last edited by a moderator: Aug 13, 2013
9. Feb 15, 2010

### haber101

Re: reaction

i appreciate the help, thanks

Last edited by a moderator: Aug 13, 2013