Fuels chem 3/4

What is a fuel

A material that can be made to react in such a way that releases useful energy

What is enthalpy

The chemical energy stored in a substance that can be converted into useful energy, measured at a constant pressure

How do you calculate energy efficiency

Useful energy produced/ total energy produced

What is the energy content of a fuel called

Heat of combustion given by KJ/g or KJ/L

What is renewability

That a substance can be replaced by natural processes in a relatively short period of time

What is carbon neutrality

The amount of CO2 released during combustion is equivalent to the amount absorbed by the plants as they grow and photosynthesise

What is sustainability

Judged based on its long term effects and to what extent the benefits outweigh the potential for undesirable effects in the future

What are economic sustainability factors

• jobs/employments

• Outgoing costs

• Ongoing availability and cost of raw materials

What are environmental sustainability factors

• Impacts of mining and extraction of raw materials

• Disturbance related to necessary infrastructure

• Waste chemicals used in processing

• Impact of combustion products

What are the social sustainability

• health impacts

• Convenience of access to consumers

• Equitable access for all

• Sociopolitical stability

• Open and productive international relations

What are the products of a complete combustion

CO2 and H2O

Products of incomplete combustion

CO or C

In combustion what is the oxidising agent

Oxygen

Characteristics of coal

• solido

• Large partially polymeric hydrocarbons

• Found Underground

• Processed minimally

• Used for electrical production and heat

Crude oil

• Liquid

• Medium to large hydrocarbons

• Found by drilling for natural deposits

• Processed by fractional distillation

• Easy to store

• Used for transport fuels

• Must be desulfured

Natural gas

• gas

• Small hydrocarbons

• Found by drilling for natural deposits

• Minimal processing required

• Hard to transport

• Used for heating and electrical production in a power plant

What is fractional distillation

When crude oil is heated in a fractioning tower, and it decreases in heat as you rise up the tower, with the smaller hydrocarbons rising higher

What is respiration

The process by which living things obtain energy from nutrients in food

aerobic respiration

Involves combining the nutrient molecules with molecular oxygen, producing carbon dioxide and water.

Anaerobic respiration

Involves reactions that do not require oxygen but typically release less energy

What are monosaccharides

The simplest carbohydrates, the most important of which is glucose

What is a disaccharide

2 monosaccharides fused together by condensation, such as sucrose or cane sugar

Polysaccharides

Condensation polymers of glucose (starch, cellulose, glycogen) used for storing

How are di and polysaccharides broken down

Hydrolysis, except for cellulose which is indigestible

How much energy is stored in a gram of carbohydrates

16KJ

What are fats

Triglycerides, which are 3 fatty acid molecules joined to a single molecule of glycerol by ester linkages

Glycerol CH2CHCH2 bonded at each carbon to a COO (ester) and the fatty acid (CH2)14CH3

How much energy is in fat

37KJ/g

What is a protein

Polypeptides formed from condensation of a large number of amino acids

How much energy is stored in protein

17KJ/g

What is biomass

Any material derived recently from living things

What is a biofuel

Any fuel derived from biomass

How is biogas produced

Anaerobic respiration by bacteria and other microbes, producing gases such as methane

Biomass → Methane + carbon dioxide + water + other produces

How is ethanol produced, and what mainly from

It is produced from glucose by yeast during fermentation using mainly corn and sugar cane as typical biomass sources

What is distillation

The process by which the solvent water is separated from the ethanol, this requires energy

Is distillation successful, and what is needed if not?

it is extremely hard to distil all of the water out of the ethanol, therefore a dehydrating agent is added to remove the final traces of water

Why is the energy content of ethanol significantly lower than that of petroleum

Ethanol is a smaller molecule containing less bonds than are in petroleum, and Ethanol has more oxidised carbons

What is biodiesel

Consists of esters of fatty acids

Why are esters of fatty acids used as fuel

As they have similar molecular size, similar boiling temperature, and similar combustion characteristics to there alkanes in normal diesel

What type of oils can be turned into biodiesel and why?

Any biological oil can, as they are made up of triglycerides, which are three fatty acid molecules ester linked to a single glycerol molecule

What is the process that turns triglycerides into biodiesel

Transesterfication, involving the heating of the fat/oil with an alcohol like methanol or ethanol in the presence of sodium hydroxide or potassium hydroxide which act as catalysts

What is made when the triglyceride is burnt with methanol

A methyl ester (R-COOCH3)

What is made when the triglyceride is burnt with ethanol

A ethylene ester (R-COOCH2CH3)

What are the draw backs of biodiesel

• Higher viscosity reducing its ability to flow through thin fuel lines, especially at low temperatures, and it can even freeze

• Tends to attract water more strongly and the higher moisture content can cause certain engine issues

When comparing biodiesel and diesel what don’t you talk about

Molecular size, as they are similar

How does energy convert from fuel to electrical when in a power station

Chemical → thermal → mechanical /kinetic → electrical

Why is the conversion rate from chemical to electrical only 40-45% in power plants

Most of the losses are heat resulting from friction in the moving parts

What formula do you use if it is SLC and you are trying to find the volume

N= V/V(m)

What is the limiting reagent

The reactant that is fully used up

What is the excess reactant

Is not completely used up, some remains, determined by n(reacted)=n(added)-n(excess)

What is enthalpy affected by

It is changed when the substance undergoes a chemical or physical change, not when the temperature increases

What causes heat energy to change

Changes in temperature

What is an exothermic reaction

When the chemical energy stored in the reactants is converted into heat energy and released

What is an endothermic reaction

Where heat energy is absorbed and converted into chemical energy stored in the products

What does forming bonds do

Reduces enthalpy and heat is released to the surroundings

What does breaking bonds do

Absorbs heat energy from the surroundings and enthalpy increases

What is the activation energy

The minimum amount of energy needed to break the bonds of the reactants and is always positive

How do you calculate enthalpy change

Delta H - H(products) - H(reactants)

What is bond energy

The energy required to break a bonds, or the energy released on forming the bond

What is a thermochemical equation

One that includes the enthalpy change

What is the equation for determine energy in a reaction

E(reaction)/n(reaction) = E(equation)/ n(equation)