Preparation of Dihydrogen by the Action of Steam on Hydrocarbons:

When steam reacts with hydrocarbons, a mixture of carbon monoxide (CO) and hydrogen gas (H2) is formed. This mixture is known as water gas.

Water Gas:
Water gas is a fuel gas composed of a mixture of carbon monoxide and hydrogen produced by passing steam over a hot carbonaceous fuel such as coal or coke. It is also known as synthesis gas or syngas.

Preparation process:
The preparation of dihydrogen by the action of steam on hydrocarbons involves the following steps:

1. Steam Reforming:
In this process, a mixture of hydrocarbon and steam is passed over a catalyst, typically nickel or iron, at high temperatures (700-1000°C). The hydrocarbon reacts with steam to form carbon monoxide and hydrogen gas.

CnH2n+2 + nH2O → nCO + (2n+1)H2

2. Water-Gas Shift Reaction:
The carbon monoxide produced in the previous step is then reacted with steam in the presence of a catalyst, usually iron oxide or chromium oxide, at temperatures around 300-400°C. This reaction converts carbon monoxide into carbon dioxide and produces additional hydrogen gas.

CO + H2O → CO2 + H2

By combining the two steps, the overall reaction can be represented as:

CnH2n+2 + nH2O → nCO2 + (2n+1)H2

Uses of Water Gas:
Water gas has several industrial applications, including:

1. Fuel:
Water gas is used as a fuel in industrial processes, such as heating furnaces and boilers. It has a high calorific value and can be used as a substitute for natural gas in some applications.

2. Chemical Synthesis:
The carbon monoxide produced in the water gas can be further processed to produce various chemicals, such as methanol, acetic acid, and ammonia. These chemicals are essential in the production of various industrial products.

3. Hydrogen Production:
The hydrogen gas produced in the water gas can be used as a feedstock for various hydrogenation reactions in the chemical industry. It is also used in the production of ammonia and as a reducing agent in metallurgical processes.

In conclusion, dihydrogen can be prepared on a commercial scale by the action of steam on hydrocarbons. This process produces a mixture of carbon monoxide and hydrogen gas known as water gas. Water gas has various industrial applications, including fuel and chemical synthesis.