Describe two characteristics of hydrogen that are favorable for its use as a general energy source in vehicles.

Hydrogen contains a high energy content per unit mass, which means that it can store more energy in a smaller amount of mass compared to other common energy sources. This characteristic is beneficial for vehicles, as it allows them to be powered efficiently without the need for large fuel storage systems. The energy content of hydrogen is approximately 120-142 MJ/kg (mega-joules per kilogram), which is much higher than that of gasoline (44-46 MJ/kg) or natural gas (50-55 MJ/kg). This high energy content allows hydrogen-powered vehicles to have a similar range as gasoline-powered vehicles, with less fuel weight.

Hydrogen is considered a clean energy source because when it is used to produce energy, the only byproduct is water. This means that hydrogen-powered vehicles have no tailpipe emissions that contribute to air pollution or climate change, which makes them more environmentally friendly than vehicles running on fossil fuels. When hydrogen is used in a fuel cell, the process involves the reaction of hydrogen with oxygen to produce electricity and water. The overall reaction can be represented by the following equation: \[2H_2 + O_2 \rightarrow 2H_2O\] This clean energy characteristic of hydrogen is especially important in the context of reducing greenhouse gas emissions and improving overall air quality in urban areas. Using hydrogen as a general energy source in vehicles can play a significant role in addressing climate change and health concerns linked to air pollution.