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.

a graduated cylinder.

explanation:

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.