What is the Balanced Equation for the Reaction between Hydrogen Gas and Oxygen Gas to Form Liquid Water?

The reaction between hydrogen gas (H2) and oxygen gas (O2) to form liquid water (H2O) is a classic example of a combustion reaction. This reaction is balanced as follows:

2H2(g) O2(g) → 2H2O(l)

In this balanced equation, 2 moles of hydrogen gas react with 1 mole of oxygen gas to produce 2 moles of liquid water. The symbol 'Δ' in chemical equations is used to denote a change or alteration. In the case of the reaction described here, 'Δ' typically indicates that heat is released during the reaction, making it a highly exothermic process. However, for clarity and consistency in writing on Quora, the symbol may not be used directly within text.

The Stoichiometry of the Reaction

The molar ratio of hydrogen to oxygen in the reaction is 2:1. This means that two molecules of hydrogen gas (H2) combine with one molecule of oxygen gas (O2) to produce two molecules of liquid water (H2O). This stoichiometry illustrates the fundamental principles of chemical equilibrium and reaction kinetics.

Theoretical and Practical Considerations

When 2 moles of liquid water (H2O) are formed by the reaction, it implies that 10 moles of dihydrogen (H2) were oxidized. This oxidation process releases a large amount of heat, which is given off as 'ΔH', representing the change in enthalpy. In the reaction, 10 moles of water are produced, which corresponds to a mass of 180 grams under standard conditions. Given that the density of water is 1 gram/mL, 180 grams of water corresponds to a volume of 180 mL.

Reaction Conditions and Enthalpy Changes

The reaction between hydrogen and oxygen to form water occurs at a very high temperature, typically at the flame temperature of hydrogen in oxygen, which is 2800°C. Under these conditions, the reaction is highly exothermic, meaning that it releases a significant amount of heat:

Change in Free Energy (ΔG2800°C) -147.9 kJ; negative value indicates the reaction is spontaneous. Change in Enthalpy (ΔH2800°C) -503.2 kJ; negative value confirms the reaction is exothermic.

The reaction will proceed spontaneously if the necessary activation energy is provided. Since the reaction is exothermic, if the heat released by the reaction is sufficient, the process can continue on its own. Catalysts, such as platinum, can be used to lower the activation energy, enabling the reaction to occur at a lower temperature.

Risk and Safety Considerations

The Hindenburg disaster, where the hydrogen-filled airship was ignited by oxygen in the air, serves as a tragic reminder of the potential risks associated with hydrogen and oxygen reactions. Ensuring proper control and safety measures when handling flammable gases is crucial.

This detailed explanation provides a comprehensive understanding of the reaction between hydrogen and oxygen to form liquid water, including the stoichiometry, theoretical considerations, and practical applications of the reaction.