2 questions with EK Chem 1001

[Spiker]

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first question:

573

Which of the following are constant throughout a single phase of any substance or mixture at equilibrium not separated by ridgid or adiabatic walls.

1. temp
2. pressure
3. mole fraction

I read this crap like 6 times and still doesnt make sense

within a single phrase temperature and pressure can both change, however number of mole doesnt change so i put C (3) however the book said D (1+2+3) explanation: temp,pressure and number of moles is enough to define a phase of a given substance. <---wtf how does that answer the question?

another thing for q 558, in the answer iodide is said to be an reducing agent....shouldn't it be oxiding agent since it accept electron?

 

[johndoe3344]

I don't have Q558 in front of me, so I don't know what it's asking, but what you're saying doesn't make sense.

Iodide is I-. If it were to be an oxidizing agent (it gets reduced itself), it is going to gain another electron to become I--. I don't believe iodine can ever take on an oxidation number of -2. It would make much more sense for it to be a reducing agent, so iodide can become iodine.

For the first part, you're correct that the properties can change within a phase, but realize the question asked for equilibrium.

Imagine a cup of milk you just heated in the microwave. Yes, there are parts that are hot and parts that are cold right after you take it out, but if you leave it out for a few hours, the entire cup of milk will be the same temperature.