Heat of combustion is always negative.

The heat of combustion of a substance, also known as the calorific value or the energy value, can be defined as the amount of heat liberated when a given amount of the substance undergoes combustion. Energy (in joules or kilojoules) liberated when one litre of the fuel undergoes complete combustion with oxygen.

Molar Heat of Combustion (molar enthalpy of combustion) of a substance is the heat liberated when 1 mole of the substance undergoes complete combustion with oxygen at constant pressure. By definition, the heat of combustion (enthalpy of combustion, ΔHc) is minus the enthalpy change for the combustion reaction, ie, -ΔH.

The heat value of a fuel is the amount of heat released during its combustion. Also referred to as energy or calorific value, heat value is a measure of a fuel’s energy density, and is expressed in energy (joules) per specified amount (e.g. kilograms). Heat value. Hydrogen (H2) 120-142 MJ/kg.

Hydrogen

A negative value indicates that the combustion is exothermic so galvanic sludge can be considered as fuel due to this relatively high value.

Fuel values are defined as the amount of energy generated by complete combustion of a particular mass of the fuel (usually one gram). It takes more energy to move larger amounts of mass; thus the higher the energy density (fuel value) the less energy is used transporting the fuel.

The calorific value of food indicates the total amount of energy, a human body could generate during its metabolism which is expressed in Kilojoules per 100 grams or 100 ml.

4 kcal/g

fats: 9.45 kcal/g. carbohydrates:4.1 kcal/g. protein:5.65kcal/g.

• It should possess high calorific value.
• It should have proper ignition temperature.
• It should not produce poisonous products during combustion.
• It should have moderate rate of combustion.
• Combustion should be easily controllable i.e., combustion of fuel should be easy to start or stop as and when required.

The most obvious fuel used in daily life runs cars, school buses and trucks. Gasoline and diesel are non-renewable fuels created from crude oil deposits in the ground or beneath the oceans. Lawnmowers and other maintenance equipment also run on gasoline.

Examples of Fuels:

Ideal fuel is the fuel which is inexpensive, it is easily available, it should have a high calorific value, it should niether burn too fast or too slow and it should leave no residue on combustion. Therefore, no fuel can be considered as an ideal fuel.

Expert Answer:

• (1) it should have high calorific value so that high amount of energy available by burning lower quantity of fuel.
• (2) easy to store and transport.
• (3) it should not produce any poisionous and polluting gases while burning.
• (4) it should not leave any harmful residue and tar after burning.

Hydrogen-fueled vehicles emit virtually no hydrocarbons, particulates, carbon dioxide, or carbon monoxide. They are viewed as an especially attractive option for reducing green house gas emissions.

Natural gas is a relatively clean burning fossil fuel Burning natural gas for energy results in fewer emissions of nearly all types of air pollutants and carbon dioxide (CO2) than burning coal or petroleum products to produce an equal amount of energy.

Answer: the fuels like CNG, LPG, biofuels are the fuels which are less polluting. Explanation: these fuels are less polluting because carbon content is lesser due to which the threat of increase of carbon in the is reduced and the stress of increase of global warming is also reduced.

CNG is more polluting fuel than petrol. Coke is almost pure form of carbon. Coal tar is a mixture of various substances.

natural gas

CNG is a natural gas stored under high pressure. Burning of natural gas produces nitrogen oxides, sulphur dioxide, carbon dioxide and carbon monoxide in low quantities than that produced during the burning of coal or oil. Thus, it is a non-polluting fuel.

Hint: Natural or non-polluting fuels are those which do not release the polluting emissions that are harmful for our environment like Methane. These fuels are renewable and are obtained from the compost or the fossil fuels. Another example is LPG. This is low in cost.