Q20.86 CP - Chemistry: Molecular Nature Of Matter And Change

Question

Is each statement true or false? If false, correct it.

(a) All spontaneous reactions occur quickly.

(b) The reverse of a spontaneous reaction is nonspontaneous.

(c) All spontaneous processes release heat.

(d) The boiling of water at ${\mathbf{100}}^{\mathbf{°}}\mathbf{\text{C}}$and 1 atm is spontaneous.

(e) If a process increases the freedom of motion of the particles of a system, the entropy of the system decreases.

(f) The energy of the universe is constant; the entropy of the universe decreases toward a minimum.

(g) All systems disperse their energy spontaneously.

(h) Both $\mathit{\Delta }{\mathit{S}}_{\mathbf{\text{sys }}}$and  $\mathit{\Delta }{\mathit{S}}_{\mathbf{\text{surr }}}$equal zero at equilibrium.

Step-by-Step Solution

Answer

a) The statement is untrue. Not all spontaneous reactions happen right away.

b) The statement is correct.

d) The statement is untrue. Heat is released by some spontaneous processes.

d) The statement is correct.

e) The statement is untrue.

The entropy of a system increases as a process increases the freedom of motion of its particles.

f) The statement is untrue.

The Universe's energy is constant, yet its entropy is increasing toward a maximum.

g) The statement is correct.

h) Statement is False. The $\Delta S_{\text{sys }}$ is equal at equilibrium.

Step 1: Definition of Delta

It is used in chemistry to indicate a change in enthalpy as well as the addition of heat to the reaction. A triangle symbol is used to represent it.

Step 2: Is statement true or false given in a)

a) 

The statement is untrue. Not all spontaneous reactions happen right away.

Some spontaneous reactions happen quickly, while others happen slowly. The speed of the reaction is not proportional to the reaction's spontaneity.

All radioactive decays, for example, are spontaneous events in which unstable isotope nuclei emit radiation as they transition to more stable nuclei. The disintegration of ${}^{238}\text{U}$ 

is not instantaneous; this is Uranium's most stable isotope, with a half-life of more than 4 billion years. 

However, ${}^{99}\text{Tc}$ is a radioactive metal that is utilised in medicine for imaging and has a half-life of roughly 6 hours.

Step 3: Is statement true or false given in b)

The statement is correct.

The reaction entropy is growing if the reaction is spontaneous in the forward direction. As a result, the entropy in the reverse direction would decrease. 

Therefore, the reverse reaction would not be spontaneous.

Step 4: Is statement true or false given in c)

c) 

The statement is untrue. Heat is released by some spontaneous processes.

Heat can be released (exothermic) or gained (endothermic) depending on the enthalpy of the process/reaction (endothermic). 

Therefore, the enthalpy of a reaction is not determined by its spontaneity.

Step 5: Is statement true or false given in d)

d) 

The statement is correct.

Water would boil at typical room pressure (1 atm) and a temperature of  ${100}^{°}\text{C}$ . When water boils, its physical state shifts from liquid to gas when molecules obtain enough energy to reattach to the liquid's surface. The kinetic energy of the water molecules in the gas (vapour) is significantly higher, and they move chaotically, increasing entropy and making the reaction spontaneous.

Step 6: Is statement true or false given in e)

e) 

The statement is untrue.

The entropy of a system increases as a process increases the freedom of motion of its particles.

As previously stated in d), as particles obtain more energy and freedom of motion, such as during evaporation.

Therefore, the system's disorder and hence entropy increases.

Step 7: Is statement true or false given in f)

f) 

The statement is untrue.

The Universe's energy is constant, yet its entropy is increasing toward a maximum.

According to the First Law of Thermodynamics, energy is conserved, hence the Universe's energy is constant. It is not lost or gained, but rather converted from one form to another.

The overall entropy of the cosmos is either rising or remaining constant, leading to a higher state of randomness/disorder, according to the Second Law of Thermodynamics.

Step 8: Is statement true or false given in g)

g) 

The statement is correct.

The Second Law of Thermodynamics can also be stated as follows: all systems' energy disperses (flows) spontaneously from more concentrated to less concentrated.

Step 9: Is statement true or false given in h)

h) 

The statement is untrue. At equilibrium, the   equals zero.

The system entropy cannot predict either rise (because it's already been maximized) or drop (because it's already been minimized) in its equilibrium condition (as by the 2nd Law of Thermodynamics, entropy is usually going towards its maximum, not the opposite). As a result, the system's entropy remains constant.

However, numerous other processes can impact the environment's entropy (i.e., everything except the system). Therefore, it can change even during the equilibrium.