[Reviction]

You guys mind assisting me with a few problems I understand others need help so I ranked them in order that I am having most problems with. I dont expect to get help with all. Just hoping one will have knowledge of one of them.

Problem 1
Under constant-volume conditions the heat of combustion of benzoic acid (HC7H5O2) is 26.38 kJ/g. A 1.570-g sample of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter increases from 22.15°C to 26.20°C.

a) What is the total heat capacity of the calorimeter?

   Ok so looking at this I see 26.38 kJ/g. Now isn't kJ/g constant-pressure calorimeter? Would I go about coverting the said problem by doing (26.38 kJ/g)(1.570g)=41.42kJ, then (ANS)(4.05 C)=167.8 kJ/C?
    What is throwing me off here is that it was burned in a bomb calorimeter whos formula is qrxn=-Ccal*t. The way I worked out that problem just now is constant-pressure. Someone mind explaining

b) A 1.400-g sample of a new organic substance is combusted in the same calorimeter. The temperature of the calorimeter increases from 21.84°C to 26.62°C. What is the heat of combustion per gram of the new substance?

Work out the same way using 26.38 kJ/g and new givens?

Problem 2
Consider the following reaction:

       CH3OH(g) → CO(g)+ 2H2(g)       ΔH = +90.7 kJ
(a) Calculate the amount of heat transferred when 1.51 kg of CH3OH(g) are decomposed by this reaction at constant pressure.

Ok I solved and came up with the answer of 4.28E3 kJ. This is not what threw me off.

b)For a given sample of CH3OH, the enthalpy change on reaction is 57.9 kJ. How many grams of hydrogen gas are produced?

Alright so how do I find the amount of grams with just 57.9kJ? I can't seem to figure out how to flip it or plug in the kJ or if I am suppose to use the information in (a).

Problem 3
(a) When a 9.55-g sample of solid sodium hydroxide dissolves in 1.00E2 g of water in a coffee-cup calorimeter (as shown in figure below), the temperature rises from 23.6°C to 47.4°C. Calculate ΔH in kJ/mol NaOH, for the solution process

NaOH(s) → Na+(aq) + OH−(aq)

Assume that the specific heat of the solution is the same as that of pure water.

Only thing I really need help on this one is the start of it. It shows 9.55g of NaOH dissolves in 100g of H2O. I forgot how to convert or whatever it is called to calculate the actual mass I will be using for the problem.


Thanks alot guys. I apperciate any help possible. I have more but thats enough for today

[LQ43]

1a) this is a constant volume problem since a bomb calorimeter was used. kJ/g doesn't indicate constant pressure. Your calculation seems to be correct

1b) take the heat capacity calculated from a) and use it in the q = equation for the new deltaT. Use it as -q and calculate -q per gram of 1.400 g of new sample

2. if 1.51 kg CH3OH reacted, how many grams of H2 were produced at the same time (stoichiometry)? if this many grams were produced with 4.28E3 kJ then this is a ratio you can use to find g of H2 with new heat given

3. q = C x mass x delta T

what is the mass of the whole sample that will be used? they are telling you to use C of pure water, you have delta T, find q

this q is released for how much NaOH? find moles of NaOh and calculate q/mol NaOH

hope that helps