Most likely the second one (sand letting water run through it) because if you are trying to determine how what moves through soil You would want the one the one that can do that:)
For your first question, that equation only works if your situation is occurring at a constant temperature. Your original question is such a situation - everything occurs at 298.15 K. Therefore, you can use this value in the equation to calculate work.
For your second question, Charles' Law describes how the volume of gas changes as you heat or cool it, PROVIDED PRESSURE AND MOLES OF GAS REMAIN CONSTANT THE WHOLE TIME. In your original question above, temperature stays constant while volume changes. However, what they don't tell you is that this necessarily requires a change in either pressure or moles of gas. Because the question works with the same sample the of gas the whole time (i.e. moles are constant), it is pressure that is changing (and this change will occur according to Boyle's Law, since temperature and moles are held constant).
Hope that clarifies things!
Answer:
<u><em>neurons</em></u>
Explanation:
The long-axoned cells, called principal neurons, transmit information over long distances from one brain region to another (Sheperd,1979). Principal neurons provide the pathways of communication within the nervous system.
Explanation :
The balanced chemical reaction is,
The expression for the rates of consumption of the reactants are:
The rate of consumption of 
= ![-\frac{1}{5}\frac{d[Br^-]}{dt}](https://tex.z-dn.net/?f=-%5Cfrac%7B1%7D%7B5%7D%5Cfrac%7Bd%5BBr%5E-%5D%7D%7Bdt%7D)
The rate of consumption of 
= ![-\frac{d[BrO_3^-]}{dt}](https://tex.z-dn.net/?f=-%5Cfrac%7Bd%5BBrO_3%5E-%5D%7D%7Bdt%7D)
The rate of consumption of 
= ![\frac{1}{6}\frac{d[H^+]}{dt}](https://tex.z-dn.net/?f=%5Cfrac%7B1%7D%7B6%7D%5Cfrac%7Bd%5BH%5E%2B%5D%7D%7Bdt%7D)
The expression for the rates of formation of the products are:
The rate of consumption of 
= ![+\frac{1}{3}\frac{d[Br_2]}{dt}](https://tex.z-dn.net/?f=%2B%5Cfrac%7B1%7D%7B3%7D%5Cfrac%7Bd%5BBr_2%5D%7D%7Bdt%7D)
The rate of consumption of 
= ![+\frac{1}{3}\frac{d[H_2O]}{dt}](https://tex.z-dn.net/?f=%2B%5Cfrac%7B1%7D%7B3%7D%5Cfrac%7Bd%5BH_2O%5D%7D%7Bdt%7D)
