R 1.3
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What is combustion?
the chemical reaction of a substance with oxygen to produce CO2 and water
What are the two important reactants for a combustion reactant?
fuel (a combustible substance) oxygen gas
Are combustion reactions exo/endothermic?
highly exothermic molecules produced are energetically stabler than reactant fuel and oxygen gas
Is an exothermic reaction positive or negative?
negative, energy is released
Is an endothermic reaction positive or negative?
positive, energy is absorbed
Which substances undergo combustion?
organic compounds many non-metals (form non-metal oxides, no fixed ratios) nearly all metals
In which state are organic compounds flammable?
they are flammable regardless of the state
What happens when organic compounds are combusted with a lack of oxygen?
incomplete combustion, may form carbon monoxide or soot
What causes the lack of oxygen in incomplete combustion?
combustion reaction occurring too quickly, depleting quantity of available oxygen around the burning fuel or limited O2 concentration
What factors may lead to incomplete combustion?
• limited O2 concentrations • low combustion temp. • large fuel particles • presence of water in solid fuels
What are observations during incomplete combustion? How does this differ from complete combustion?
releasing smoke producing an orange or yellow flame when enough oxygen is present, flame is much hotter and bluer, and there is no smoke formed
What defines the products in incomplete combustion?
the less oxygen you have, the lower ratio of carbon-oxygen atoms CO2 –> CO –> C
What are fossil fuels?
mixtures of many compounds that formed through the decomposition of prehistoric organisms over time, deep within the Earth’s crust
Are fossil fuels pure?
no - comprise of a range of compounds, not just one
In which 3 main categories are fossil fuels divided into?
coal, crude oil, and natural gas
What is coal’s composition and state at room temp?
Mainly carbon - traces of H, O, N, S and metals solid
What is crude oil’s composition and state at room temp?
Mixture of medium/long chain hydrocarbons - traces of S, N, O and metals liquid
What is natural gas’s composition and state at room temp?
Mostly methane - traces of small hydrocarbons, H2O, CO2 gas
What are advantages of fossil fuels?
• highly exothermic when combusted • relatively easy to transport, convenient • abundant in many countries • relatively inexpensive to obtain compared to set-up costs • boost economy, jobs, income, taxes • support industries such as agriculture, manufacturing and power generation
What are disadvantages of fossil fuels?
• mining, transport, and processing is harmful to local and global environments • threat of oil spills, pipeline leaks, cole mine explosions • burning produces substances harmful for health and environment • global warming • respiratory problems • acidification of lakes and soil • non-renewable
What is the greenhouse effect?
a phenomenon that occurs when certain gases such as CO2, methane or NOx absorb infrared radiation. this IR radiation has been emitted from the earths surface after being heated by the sun. greenhouse gases then emit the IR radiation in all directions, so more energy is trapped within the atmosphere, leading to higher temperatures
Which types of fuel release least/more CO2?
most - coal middle - crude oil least - natural gas
How can one calculate the mol of CO2 produced per MJ of energy?
mol CO2/kJ of energy released per mol * 1000
Which types of fuels produce the least/most volume of CO2?
most - coal middle - crude oil least - natural gas