Select the statements below that are false and think about why they are not true.

a) If a chemical reaction is spontaneous then the? Ssys must always be positive.

b) If a chemical reaction with a negative? Ssys is spontaneous then? Ssurr must be positive.

c) If a chemical reaction is spontaneous then the? Euniv must be increasing.

d) We don/'t need to worry about spontaneous reactions because they are rare.

a) and d) are false.

Explanation:

a) The second law of thermodynamics states that the entropy of the universe increases in a spon taneous process and remains unchanged in an equilibrium process.

For a spontaneous process:

ΔSuniv = ΔSsys + ΔSsurr > 0

For a spontaneous process, the second law says that ΔSuniv must be greater than zero, but it does not place a restriction on either ΔSsys or ΔSsurr. Thus, it is possible for either ΔSsys or ΔSsurr to be negative, as long as the sum of these two quantities is greater than zero.

d) A reaction that does occur under the given set of conditions is called a spontaneous reaction. We observe spontaneous physical and chemical processes every day, including many of the following examples:

• A waterfall runs downhill, but never up, spontaneously.

• A lump of sugar spontaneously dissolves in a cup of coffee, but dissolved sugar does not spontaneously reappear in its original form.

• Heat flows from a hotter object to a colder one, but the reverse never happens spontaneously.