Question

In which of the following chemical equations, the abbreviation represent the correct states of the reactants and products involved in reaction temperature?
A. $2H_2\left(l\right)+O_2\left(l\right)\to 2H_{2}O\left(g\right)$
B. $2H_2\left(l\right)+O_2\left(l\right)\to 2H_{2}O\left(l\right)$
C. $2H_2\left(g\right)+O_2\left(g\right)\to 2H_{2}O\left(l\right)$
D. $2H_2\left(g\right)+O_2\left(g\right)\to 2H_{2}O\left(g\right)$

Answer 1

Hint: We know that two reactants in different phases combine to produce a new compound. The new compound formed could be present in any phase that is gas, solid, and liquid. We have to know that the state of a substance at a specific temperature & pressure is dependent on how adjacent the molecules of that substance are which depend on how strong the intermolecular force is and the conditions of temperature and pressure.

Complete step by step answer:
Oxygen and Hydrogen in elemental form are found as gases at room temperature less than one atmosphere. But water is found as liquid at room temperature less than 1 atmosphere.
We know that Hydrogen and oxygen combine to yield water $\left(H_{2}O\right)$. But the intermolecular force of attraction present between molecules of water is stronger than the intermolecular forces present between hydrogen $\left(H_2\right)$molecules and the intermolecular forces present between oxygen molecules $\left(O_2\right)$.
So, molecules of water are closer to each other than molecules of hydrogen and oxygen and are found as liquid while oxygen and hydrogen are found as gases under conditions of same temperature and pressure.
We can write the chemical reaction between gaseous hydrogen and gaseous oxygen as,
$2H_2\left(g\right)+O_2\left(g\right)\to 2H_{2}O\left(l\right)$
$2H_2\left(g\right)+O_2\left(g\right)\to 2H_{2}O\left(l\right)$ is the correction reaction since during formation of water both hydrogen and oxygen are present in gaseous form and water is formed in liquid state.

Therefore, the option (C) is correct.

Note:
We can say the formation of liquid water from gaseous hydrogen and gaseous oxygen as a combination, exothermic, and redox reaction.
We call the formation of liquid water a combination reaction because two reactants (hydrogen and oxygen) combine to form a single product (water).
Since, heat is liberated out during the formation of water; we call it an exothermic reaction.
In the formation of water, the transfer of electrons takes place from hydrogen to oxygen, so Oxygen is reduced and electrons are accepted by oxygen from hydrogen, so Hydrogen is oxidized. Since oxidation and reduction simultaneously happen, we call it a redox reaction.