thermochemistry chem conceptual.
i just want to check my understanding of this
Say you got this:
1)A + b=c
A=4.0 grams
and -91.8kj evolve
How do you find change of H ?
I guess you convert A to grams and then shove it under the evolved heat ? ie. change of H= -91.8kj/2 mol=
2)Now if i want to find heat of formation of C I just use the books values and then use algebra ?
Say book values for B=-290 and A=-197
A + b=c change of H= -46kj/mol
[(-197)+(-290)]- x = -46kj/mol
-x=441kj/mol
x=-441
hope you understand this )
I understand you have no idea what you are doing.
first: the 4 grams only has to do with how much (you can convert it to moles).
Second: Hf(of C)=Hreaction-Hf(ofA)-Hf(ofB) all on a per mole basis.
Now if there are coefficients of A or B, you have to multipy those coefficients by the Hf(or A or B).
I would suggest review your text materials, this concept is not difficult. You apparently are stuck on something.
what ?
This is from a test. I don't remember the numbers. The teacher never explained it so im trying to find a method to do it.
In part A we are asked to find the change of heat. Change of heat =standard heat of formation. (H with the little circle)
At this point i don't know what the evolved heat equals. Does it equal the q(heat)of surrondings or reaction?
So to find change of heat i got to find the moles of the limiting reagent. Since the mole ration are the same for the reactants it equals moles of A.
So throw it under the evolved heat to find change H=standard H
B) find x. Plug in the standard heat of formations for the ones i know. Then use algebra ?
To find the change in enthalpy (ΔH) for the reaction A + B = C, you need to use the given information about the mass of A and the evolved heat. Here's how you can do it:
1) Convert the mass of A to moles:
To convert the mass of A (4.0 grams) to moles, you need to know the molar mass of A. Assuming you have the molar mass, divide the mass by the molar mass to get the number of moles of A.
2) Use the moles of A to calculate ΔH:
Since the reaction equation is not balanced and you don't have the stoichiometric coefficients, you cannot directly determine the change in enthalpy. However, you can calculate the heat evolved per mole of A by dividing the given evolved heat (-91.8 kJ) by the number of moles of A. This will give you the heat evolved per mole of A.
For example, if 4.0 grams is equivalent to 0.05 moles of A, then the change in enthalpy would be:
ΔH = (-91.8 kJ) / (0.05 mol) = -1836 kJ/mol of A
Regarding finding the heat of formation of C, you cannot directly use the book values for A and B and then use algebra to determine the heat of formation. Heat of formation (ΔHf) is the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
If you want to find the heat of formation of C, you need specific data on the heat of formation of A and B, as well as the balanced chemical equation for the reaction of A and B to form C. Then, you can use Hess's law or other thermodynamic relationships to calculate ΔHf for C based on the given heat changes for A and B.
It's important to note that you need complete and accurate information (such as balanced equations and thermodynamic values) to properly calculate thermodynamic quantities.