Explanation :
In thermodynamics, a system is region or part of space which is being studied and observed while the surrounding is the region or space around the system which interacts with the system.
Here in the experiment ,system which is observed is reaction or changes when citric acid and sodium bicarbonate are mixed together. And the mixing is carried out in the calorimeter which serves as a surrounding around the system.
The reason behind the using the calorimeter is measure the energy change occurring during the reaction.
Answer: The space occupied by the gas at 400 torr and 
is 250 mL.
Explanation:
Given: 
= 250 mL, 
= 800 torr, 
, 
= 400 torr, 
Formula used is as follows.
Substitute the values into above formula as follows.
Thus, we can conclude that space occupied by the gas at 400 torr and is 250 mL.
Answer: one molecule of O2.
Explanation: sweet i just took a guess but I believe that if 3 o2 molecules - 2 h2 molecules I think that its just basic maths and it is C because 3-2 = 1 and its o2 remaining, sorry if I’m wrong.
Right now it's written in scientific notation, so you can just move the decimal place in 3.8 to the right 3 times (as it is times 10 to the third power) to get 3,800g.
More energy than atoms in a liquid state
