Chemistry, 31.08.2019 02:10 sidneylww

Asample consisting of 2 moles he is expanded isothermally at 0 degrees from 5.0dm3 to 20.0dm3. calculate w, q and deltau for each of the following situations: (i) a reversible expansion of the sample. (ii) an irreversible expansion of the sample against a constant external pressure equal to the final pressure of the gas. (iii) a free expansion (against zero external pressure i. e. in a vacuum) of the sample.

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Answer from: abbygutierrez401

i) $\Delta U=0 w=-6293 J q=6293 J$

ii) $\Delta U=0 w=-3404,52 J q=3404,52 J$

ii) $\Delta U=0 w=0 J q=0 J$

Explanation:

As the initial and final states of the sample are the same, the ΔU of the sample is, for the three cases

$\Delta U=n.C_{V}.\Delta T=0$ since $\Delta T=0$

i)Reversibly $P_{ext} =P_{sys}$ so can be calculated by

$w=-n.R.T.ln(\frac{V_{f}}{V_{i}})=-2 \times 8.314\frac{J}{mol K} \times 273,15K \times ln(\frac{}{5dm^{3}})=-6293 J$

and because of the first law of thermodynamics

q=-w=6293 J

ii)Irreversibly with $P_{ext} =P_{f}$

we can calculate $P_{f}$ by the law of ideal gases

$P_{f} =\frac{n\times R\times T}{V_{f}} =\frac{2\times 0.082\frac{dm^{3}atm}{mol K}\times 273,15K}{20dm^{3}} =2,24 atm$

then w can be calculated by

$w=-P_{ext} \times \Delta V=-2,24 atm \times (20-5) dm^{3} \times frac{101.325J }{atm dm^{3}=-3404,52J$

and

q=-w=3404,52J

iii)a free expansion $P_{ext}$ so w=0 (there's no work at vaccum) and q=-w=0

Answer from: Quest

the answer

explanation:

the capillary tube was too close to the bottom of the beaker.

the ruler may have moved.

water got into the capillary tube.

the temperature was not allowed to equilibrate in the 2-4 minutes.

Answer from: Quest

water molecules stay close to each other through cohesion, the collective action of hydrogen bonds between water molecules. cohesion plants draw water upwards from the root through the stem's transport tubes (xylem) to the leaf. this transport occurs even in large trees and against gravity. transpiration, evaporation of water from plant leaves, creates a tension on water molecules being pulled up from the stem and roots.

water also has high (the attraction of one substance to another) properties because of its polar nature. adhesion of water molecules to plant cell walls counteract gravity while water is transported from roots to leaves.

water exhibits a very high surface tension when compared to other liquids. surface tension is a property of a liquid that holds the surface together and allows it to resist an external force. by capillary action, the water forms concave menisci inside the pores. the high surface tension of water pulls the concavity outwards, generating enough force to lift water from the roots to the leaves of plants.

thus, cohesion, along with adhesion and surface tension creates a capillary action that keeps water molecules interacting and moving through the plants out to the leaf cells.

therefore, option d) is the correct answer.

explanation: