Question

Which of the following processes are spontaneous and which are nonspontaneous: (a) the ripening of a banana, (b) dissolution of sugar in a cup of hot coffee, \((\mathrm{c})\) the reaction of nitrogen atoms to form \(\mathrm{N}_{2}\) molecules at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{~atm},\) (d) lightning, (e) formation of \(\mathrm{CH}_{4}\) and \(\mathrm{O}_{2}\) molecules from \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) at room temperature and 1 atm of pressure?

Short answer

In short, the following processes are spontaneous: (a) ripening of a banana, (b) dissolution of sugar in hot coffee, (c) formation of N2 molecules at 25°C and 1 atm, and (d) lightning. The only non-spontaneous process is (e) formation of CH4 and O2 from CO2 and H2O at room temperature and 1 atm.

Step-by-step solution

1. (a) The ripening of a banana

Ripening of fruits, like a banana, is a spontaneous process. It is a natural occurrence and requires no external intervention for it to happen. Fruits ripen due to the production of ethylene, a plant hormone that regulates fruit maturity.

2. (b) Dissolution of sugar in hot coffee

The dissolution of sugar in hot coffee is also a spontaneous process. As the temperature of the coffee is higher, it increases the solubility of sugar. Increased motion of molecules due to heat allows the sugar to dissolve more easily. Stirring may speed up the process, but it is not necessary for the sugar to dissolve.

3. (c) Formation of N2 molecules at 25°C and 1 atm

The formation of dinitrogen (N2) molecules from individual nitrogen atoms at 25°C and 1 atm is spontaneous. Triple-bonded diatomic nitrogen is a highly stable compound, so nitrogen atoms tend to form these molecules naturally when given the chance.

4. (d) Lightning

Lightning is a spontaneous process. It occurs naturally as a result of the separation of electric charges in storm clouds and the buildup of static electricity, which leads to a sudden discharge of electrical energy.

5. (e) Formation of CH4 and O2 from CO2 and H2O at room temperature and 1 atm

The formation of methane (CH4) and oxygen (O2) molecules from carbon dioxide (CO2) and water (H2O) at room temperature and 1 atm pressure is non-spontaneous. This reaction requires an external energy source, such as sunlight in photosynthesis, to break strong bonds in CO2 and H2O and form the bonds in CH4 and O2. In the absence of an energy input (e.g., sunlight), the reaction will not occur spontaneously. To summarize: 1. The ripening of a banana is a spontaneous process. 2. Dissolution of sugar in hot coffee is a spontaneous process. 3. Formation of N2 molecules at 25°C and 1 atm is a spontaneous process. 4. Lightning is a spontaneous process. 5. Formation of CH4 and O2 from CO2 and H2O at room temperature and 1 atm is a non-spontaneous process.

Key concepts

Chemical Reactions

Chemical reactions are transformations involving the reorganization of atoms in substances, leading to the formation of new products. These processes can either be spontaneous or non-spontaneous.
An example of a spontaneous reaction is the ripening of fruits, such as bananas. This occurs naturally as a result of internal chemical changes involving ethylene gas, a plant hormone that accelerates fruit maturity without any external help.
On the other hand, some reactions, like the formation of methane (CH extsubscript{4}) and oxygen (O extsubscript{2}) from carbon dioxide (CO extsubscript{2}) and water (H extsubscript{2}O), need external energy input because the process is non-spontaneous under standard conditions (room temperature and 1 atm). Without energy, such as that from sunlight in photosynthesis, these chemical changes do not occur on their own.

Thermodynamics

Thermodynamics in chemistry deals with the study of energy changes during chemical reactions and processes. It helps us understand why certain processes are spontaneous.
Take, for instance, the dissolution of sugar in hot coffee. This process is spontaneous because of thermodynamic principles. The increase in temperature leads to higher kinetic energy, causing sugar molecules to disperse more readily in the solvent, i.e., coffee.

• This dispersion results in an increase in entropy (disorder), which is a key factor in making the process spontaneous.
• Lightning is another spontaneous thermodynamic process that occurs due to charge separation and buildup, ultimately releasing energy as a spectacular discharge.

Thus, thermodynamics is crucial in understanding how energy transformations lead to spontaneous processes in nature.

Chemical Stability

Chemical stability is the tendency of a chemical substance to resist change or decomposition. Substances with high stability have strong bonds and are less reactive.
Consider nitrogen molecules ( ext{N} extsubscript{2}), which are formed from nitrogen atoms. The ext{N} extsubscript{2} molecule has a triple bond and is one of the most stable diatomic molecules. It forms spontaneously because the resulting ext{N} extsubscript{2} structure is significantly more stable than isolated nitrogen atoms due to its strong bond.

• Stability is also why oxygen in the air doesn’t convert into a different compound spontaneously, as it would require substantial energy input to break the stable ext{O} extsubscript{2} bonds.

Understanding chemical stability is essential in predicting the behavior of substances and their propensity to undergo chemical changes.