Question

As an ionic solid dissolves in water, the temperature of the solution increases. What best describes the enthalpy and entropy of the solution?

A. The enthalpy change is positive, and the entropy increases.
B. The enthalpy change is negative, and the entropy decreases.
C. The enthalpy change is positive, and the entropy decreases.
D. The enthalpy change is negative, and the entropy increases.

Answer 1

@JFraser It's B right?

Answer 2

it's not B.

You \(know\) that the temp increases, so the reaction is exothermic.

What do you know about the \(disorder\) of a dissolving ionic solute in water?

Answer 3

Ohh so if the temp increases, it has to be A or C right?

Answer 4

when the temperature of the \(water\) increases during dissolving, it's really part of the surroundings, not the system.

the ionic solute is \(releasing\) energy into the water, which is what makes the temp increase.

Answer 5

Hmm ok so what would the answer be?

Answer 6

when the temperature of the surroundings increases, energy is leaving the system and we call the reaction \(exothermic\). What's the sign of \(\Delta H\) for an exothermic reaction?

Answer 7

I'm not sure

Answer 8

if you've done anything with enthalpy or heat movement before, this is one of those things you HAVE TO know. Can you find it somewhere?

Answer 9

Positive sign

Answer 10

So is the answer C? @JFraser

Answer 11

@dtan5457 it's C right?

Answer 12

it's not C

Answer 13

Are you sure? Then it must be D then?

Answer 14

the enthalpy sign of an exothermic reaction is \(negative\), and the entropy sign of a dissolving process is \(positive\)

Answer 15

Ok so is the answer D?

Answer 16

it is

Answer 17

thanks