Carbon-based fuels

• Combustion reaction is a reaction in which a substance reacts with oxygen gas to produce energy in the form of light and heat.
• Exothermic reaction release energy into the environment. Therefore, it has a negative enthalpy value as energy is lost. The reactants have a higher enthalpy value then the product
• Endothermic reaction absorb energy from the environment. Therefore, it has a positive enthalpy value as energy is gained. The products have a higher enthalpy value then the reactants
• Heat energy or enthalpy (H) refers to the chemical energy of a substance, or the amount of energy stored in the bonds of atoms and molecules.
• Enthalpy change (ΔH) is the difference between the total enthalpies of products and reactants. It is determined by subtracting the enthalpy of the reactants from the products
• Activation energy is the required amount energy to break the bonds of the reactants so that a reaction can occur.
• Thermochemical reaction includes the change in enthalpy value for a reaction between the reactants and products
• When reading an energy profile diagram activation energy is the different in the reactant and peak height while the change in enthalpy is the difference in reactants and products. Activation energy occurs first
• A fuel is a substance with stored energy that can be released relatively easily for use as heat or power
• A fuel is considered non-renewable if it can not be replenished at the same rate at which it is consumed. While renewable fuel can be replenished at a sustained rate.
• Fossil fuels are formed from the remains of dead organisms that still retain chemical energy that the plants originally accumulated through photosynthesis.
• Crude oil is a mixture of hydrocarbon molecules that can be separated into a range of fractions through fractional distillation. This can produce petrol which can undergo a combustion reaction to release thermal energy.
• Biofuels are fuels derived from organic material as they are produced from plants, biofuels are said to be carbon neutral as the carbon dioxide released is reabsorbed through photosynthesis by the plants.
• Biodiesel is formed through the warming of fats and oils using alcohol in a process called transesferication. Bases like KOH is used to catalyst the reaction
• Photosynthesis is an endothermic reaction carried out in the chloroplast as sunlight is absorbed and is used to power the reaction.
• Cellular respiration is the process of burning glucose in the presence of oxygen to release energy, as such, it is also a form of combustion meaning it is an exothermic reaction
• Fats and oils produce more energy then carbohydrates and proteins as they have less oxygen molecules. As such, carbohydrates undergo partial oxidation before they they are used. While fats and oils are able to fully oxidise and produce more energy.
• Complete combustion occurs when there is sufficient oxygen available during combustion. All of the fuel will react completely with oxygen producing only water vapour and carbon dioxide as products.
• Incomplete combustion occurs when there isn't enough oxygen present during combustion. In this case, not all of the fuel will react with oxygen so some unburnt fuel remains. The remaining fuel can be carbon monoxide
• heat of combustion is the heat energy released when a specified amount of substance burns completely in oxygen
• Enthalpy of combustion a negative value but with the same numerical value as the heat of combustion
• Distillation is a process that utilises different boiling points of liquids and is used to separate them. Liquids with higher boiling points condenses at the bottom and gradually decreases upwards
• Bioethanol is produced through fermentation when enzymes and other microorganisms break down sugars and catalyse the reaction