Question

Indicate whether the entropy of the system increases, decreases, or is unchanged for each of the following processes:

a) water evaporates at room temperature

b) a gas condenses at its normal boiling point

c) cold water is heated to 120 F by a natural gas heater

d) water vapor forms ice crystals (frost) on your car's windshield

e) CH4(g) + 2O2(g)<----> CO2(g)+ 2H2O(l)

Answer 1

First lets remember the definiton of entropy

By definition entropy is  a measure of the number of specific realizations or microstates that may realize a thermodynamic system in a defined state specified by macroscopic variables. Most understand entropy as a measure of molecular disorder within a macroscopic system,

In other words we can see entropy as the movement freedom that the molecules have in the state they are. For example. water. when is solid, the molecules are in a state where they have no movement at all, when liquid they have more movement, but in gaseous state they are completly free, so the bigger the entropy.

Now lets discusse our systems:

a) if we have liquid that evaporates to gas, the entropy of the system increases because of the freedom of movemen in gaseous state is greater than in liquid.

B) when a gas condenses, it goes for the greater entropy they could have to an state where their movement is a little more limited. thus the entropy decreases.

C) i whe have cold water it is in solid state (the smaller entropy state) and is heated it will pass to a state withless density, then the molecules will move freely, then the entropy increases.

D) if the water vapor forms ice crystals, then it goes from gaseous to solid state, then the entropy of the system decreases.

e) When we have a reaction where in one side we have all the molecules in gaseous state, and in the other side we have only one molecule in gaseous state, the greater entropy will be in the side with more moles (because there are more particules moving around)

Then in this reaction we have 1 mol of methane and 2 moles of oxygen that forms one mole of carbon dioxide, In one side we have 3 moles of reactants and in the other side we have 1 mole o products, then the entropy decreases because there are less moles in the products side.