Question

For each of the questions, four choices have been provided. Select the correct alternative. Which among the following reactions is an example of instantaneous reaction under normal conditions? (a) \(2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{N}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{NO}\) (c) \(\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\)

Short answer

a) \(2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\) b) \(\mathrm{N}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{NO}\) c) $\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}$ d) $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$ Answer: c) $\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}$

Step-by-step solution

Examine Reaction (a)

First, we consider the reaction between hydrogen gas and oxygen gas to form water: \(2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\) This reaction is exothermic but is not an example of an instantaneous reaction under normal conditions, as it requires activation energy to initiate the reaction.

Examine Reaction (b)

Next, we consider the reaction between nitrogen gas and oxygen gas to form nitrogen monoxide: \(\mathrm{N}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{NO}\) This reaction is also not instantaneous under normal conditions, as the activation energy for this reaction is high and requires high temperatures to occur.

Examine Reaction (c)

Now, we consider the reaction between sodium hydroxide and hydrochloric acid to form sodium chloride and water: $\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}$ This reaction is an acid-base neutralization reaction and does proceed quickly under normal conditions. This could be the correct answer as it's known to be near-instantaneous.

Examine Reaction (d)

Finally, we consider the reaction between sucrose and water to form glucose and fructose: $\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$ This reaction is the hydrolysis of sucrose and requires a catalyst like an enzyme for it to occur rapidly. Under normal conditions, without a proper catalyst, it can be slow. Step 2: Choose the correct reaction

Determine the instantaneous reaction

Based on the analysis of the given reactions, the reaction between sodium hydroxide and hydrochloric acid (c): $\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}$ is an example of an instantaneous reaction under normal conditions. It proceeds rapidly, unlike the other reactions which require higher activation energy or catalysts to occur quickly. So, the correct answer is (c).

Key concepts

Chemical Reaction Rates

Understanding chemical reaction rates is an essential part of predicting how quick or slow a chemical process will occur. This concept is tied to the speed at which reactants are transformed into products during a chemical reaction. Several factors influence these rates, including concentration, temperature, surface area, catalysts, and the nature of reactants.

For instance, an increase in the concentration of reactants generally accelerates the rate, providing more particles that can collide and react. Similarly, higher temperatures boost the energy of particles, which also speeds up reactions. A catalyst, without being consumed in the reaction itself, can lower the activation energy required for the reaction to proceed, effectively increasing the rate. In academic exercises, students are often asked to identify which reactions occur quickly or instantaneously under normal conditions, emphasizing the practical implications of reaction rates.

Activation Energy

Activation energy is a crucial threshold energy that reactants must overcome for a chemical reaction to occur. It's like a barrier—without the necessary energy to surpass this barrier, the reactants simply won't turn into products.

Activation energy is affected by various factors including the nature of the molecules and the environment in which the reaction takes place. Catalysts play a key role in lowering this energy barrier and can be a pivotal concept in exercises aimed at understanding why certain reactions don't happen instantaneously under normal conditions. Learning how activation energy impacts reaction rates offers students a deeper insight into the kinetics of chemical reactions.

Acid-Base Neutralization

Acid-base neutralization reactions are a form of double displacement reactions where an acid reacts with a base to produce salt and water. A recognizable example is the reaction between sodium hydroxide (a base) and hydrochloric acid to form sodium chloride (table salt) and water.

These reactions are often exothermic, releasing heat as they proceed rapidly, sometimes even instantaneously. A common application of this concept is in titration procedures, which are instrumental in determining the concentration of an acidic or basic solution. This principle of rapid reaction is highly relevant when identifying the instant nature of certain reactions under normal conditions in exercises.

Exothermic Reactions

Exothermic reactions are chemical processes that release energy, usually in the form of heat, to the surroundings. This release occurs because the total energy of the products is less than that of the reactants; the difference in energy is expelled as heat or light.

Typical examples include combustion reactions, such as the burning of wood or natural gas, and acid-base neutralizations. The concept of exothermic reactions is not only an interesting topic in exercises but also has real-world significance, as it is fundamental in the understanding of energy production, such as in power plants and hand warmers. Exothermic reactions are often contrasted with endothermic reactions that absorb energy, requiring a continuous input of heat to sustain the reaction.