Unit 4 Fuels, combustion Flashcards
Exothermic and Endothermic reactions + energy profiles (check pics after answer)
Exothermic: Releases energy in the form of heat. (mnemonic exo: exit thermal: heat)
eg: Burning fuels, forming bonds
Energy profile: Reactants start with a higher amount of energy than the products. This means that the reactants have more energy stored in their chemical bonds than the products. As the reaction proceeds, and the reactants get the energy they need (reach Transition State) the reaction starts and energy is released, usually in the form of heat, causing the energy of the system to decrease.
Endothermic: Absorbs energy from its surroundings usually in the form of heat. (mnemonic endo: enter thermal: heat)
eg: Photosynthesis (absorbs energy from the sun), Melting ice, breaking bonds
Energy profile:
Reactants start with a lower amount of energy than the products. This means that the reactants have less energy stored in their chemical bonds than the products. As the reaction proceeds and the reactants get the energy they need (reach Transition State), energy is absorbed from the surroundings, usually in the form of heat, causing the energy of the system to increase.
Hydrocarbons and Fossil Fuels + Significance + Environmental Concerns
Hydrocarbons are organic compounds that are entirely made up of only two kinds of atoms –
A fuel is a substance that releases energy in an exothermic reaction (can used to start a fire).
.
Fossil fuels are non-renewable energy sources mostly made of hydrocarbons. They are formed by decomposing dead and decaying(متحللة) plant or animal matter underground
for millions of years.
eg: include coal, oil (petroleum), natural gas.
Safety: High activation energy make them don’t combust spontaneously.(safe for storage or transportation)
Efficiency: Fuels with appropriate activation energy levels burn more efficiently. too low might lead to incomplete combustion, too high means fuel doesn’t burn easily
When burned, fossil fuels release Carbon dioxide, water, heat, and light as with other greenhouse gases, contributing to air pollution, and climate change (global warming).
Fire triangle + Complete and incomplete combustion of fossil fuels
When burned (after combustion reaction), fossil fuels release Carbon dioxide, water, heat, and light as with other greenhouse gases, contributing to air pollution, and climate change (global warming).
Fire triangle:
Oxygen, heat, and a fuel are needed to start a fire.
Complete combustion:
Occurs when there is excess to sufficient oxygen to complete the reaction.
equation eg: combustion for propane (a gas that is commonly used at homes for cooking):
C3H8 + 5O2 → 3CO2 + 4H2O
Propane + Oxygen → Carbon Dioxide + Water
Incomplete combustion:
Occurs when there isn’t enough O2. produces unburnt fuels (soot), CO (Carbon monoxide), and water.
Carbon monoxide is a toxic gas that can produce a bad smell, and cause dizziness, loss of consciousness, and even death.
eg: Methane incomplete combustion:
CH4+O2→CO+H2O+C
Methane + Oxygen → Carbon Monoxide + Water + Carbon
Identifying oxidizing and reducing agents in a combustion reaction.
Great mnemonic:
Oil Rig: Oxidation is loss; Reduction is gain (of electrons).
Oxidizing agents (accept electrons):
Causes another substance to be oxidized (loses electrons).
Oxygen is the primary oxidizing agent in a combustion reaction. It accepts electrons from the substance being burned and is reduced (takes in electrons) to form water or carbon dioxide.
Reducing Agents (loses electrons):
Causes another substance to be reduced (gains electrons).
In a combustion reaction, the fossil fuels act as the reducing agent being oxidized itself.
Eg to oxidizing and reducing:
CH4+O2→CO+H2O+C
Methane + Oxygen → Carbon Monoxide + Water + Carbon
Methane is the reducing agent being oxidized.
Oxygen is the oxidizing agent being reduced.
How does a lithium battery work and why is it more eco-friendly than fossil fuels?
It produces energy without emitting greenhouse gases or pollutants.
In lithium Ion batteries the anode is made up of graphite which acts as the storage and attracts electrons as it is positive.
The cathode is made up of lithium metal (like cobalt) oxide.
The electrolyte is a lithium salt dissolved in a solvent. It acts like a gourd that only allows lithium ions to get in.
During charging: Lithium electrons in the lithium metal oxide get free because of oxidation, they will get attracted to the positive side of the battery so they go there. the lithium ions will get attracted to the new negative side so they will go through the electrolyte to the graphite.
During discharging: Lithium electrons will go back to the cathode powering the electrical device and then the lithium ions will go through the electrolyte again bonding with the metal oxide.
Fractional distillation of crude oil
Simple Distillation: Heating the mixture to turn one part into vapor, then cooling it down to turn it back into liquid, leaving behind the other part. boiling points with a gap of a minimum of 50 degrees.
Fractional distillation of crude oil:
1) Crude oil is heated in a furnace to temperatures ranging from 350 to 400°C.
2) After heating it vaporizes, forming a mixture of hydrocarbon vapors.
3) Vaporized crude oil is then passed into a tall fractionating column, which is hotter at the bottom and cooler at the top.
4) Different hydrocarbon components condense at different heights within the column based on their boiling points.
5) Separated hydrocarbon fractions are collected at different levels of the column.
After the process of fractional distillation they won’t be used, fossil fuels still need purification and refinement.
Hydrogen fuel cells
Cats sleep, fish eat lonely.
Cathode site for electron loss. (reduction)
Ants sleep, fish eat grains.
Anode Site for electron gain. (oxidation)
Hydrogen fuel cells:
Devices that convert the chemical energy of hydrogen (H2) and oxygen into electricity through an electrochemical process.
Process:
1) Hydrogen gas (H2) is supplied to the anode of the fuel cell.
2) Electrochemical Reaction: At the anode, hydrogen molecules are split into protons (H+) and electrons (e^-) through oxidation.
3) Electron Flow: Electrons flow through an external circuit, creating an electric current that can power devices.
4) Proton Movement: Protons travel through an electrolyte to the cathode.
5) Oxygen Input: Oxygen gas (O2) from the air is supplied to the cathode.
6) Electrochemical Reaction: At the cathode, oxygen combines with electrons and protons to form water (H2O) through reduction.
7) Electricity Output: The flow of electrons through the external circuit generates electrical power.
The only byproduct of the process is water vapor, which is released from the fuel cell.
Advantages:
1)Does not produce any pollution.
2)produce more energy than petrol or diesel.
Disadvantages:
1)Materials used in production are expensive.
2) Fuel cells become less efficient at low temperatures.
3) Hydrogen is expensive to produce and store.
4) High-pressure tanks that store oxygen and hydrogen are dangerous and difficult to handle.
Nuclear fission
nuclear fission:
The process of when the nucleus of an atom splits into smaller parts, releasing a lot of energy that can be used. low-carbon alternative to fossil fuels and can play a role in reducing greenhouse gas emissions. It has its own challenges.
