Calculate δh (in kj) for the process hg2br2(s) → 2 hg(l) + br2(l) from the following information.
hg(l) + br2(l) → hgbr2(s) δh⁰298 = −170.7 kj
hg(l) + hgbr2(s) → hg2br2(s) δh⁰298 = −36.2 kj

Answer : The enthalpy change of reaction is 206.9 kJ

Explanation :

According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.

According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.

The given final reaction is,

The intermediate balanced chemical reaction will be,

(1)    

(2)    

First we will reverse the reaction 1 and 2 then adding both the equation, we get :

(1)    

(2)    

The expression for final enthalpy is,

Therefore, the enthalpy change of reaction is 206.9 kJ

send me question so i can u

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.