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Energetics (Calculating enthalpy changes (Calculation (*experimental…
Energetics
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Hydrogen
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No deposits of hydrogen available – has to be produced from water – requires energy from another source
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Carbon dioxide
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Prepared in a lab by marble chips (calcium carbonate) and dilute HCl
CaCO3 – 2HCl –––> CaCl2 + H2O + CO2
Uses:
Fire extinguisher – denser than air, stops oxygen reaching combusting material
Carbonated drinks – dissolved under high pressure, slowly bubbles out
Measuring energy changes
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Types of energy changes
of combustion: the energy change when one mole of a particular fuel is burned fully in oxygen under standard conditions
of neutralisation: the ∆H when one mole of an acidis fully neutralised in solution by an alkali
–> H+ + OH- –––> H2O
of solution: ∆H when one mole of a particular substance is dissolved in water (to give a conc of 1mol/dm3)
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Lefty clap-trap
Pollutants from fuels
Sulfur dioxide
Dissolves in water vapour to make sulfurous acid (H2SO3)
–> may later oxidise to form sulfuric acid – H2SO4
Fall as acid rain: damaging trees, crops and stone buildings,
killing plants and animals in lakes and rivers
Forms as a result of burning fuels containing sulfur compound impurities
–> can be removed by bubbling waste gases through an alkaline solution
Nitrogen oxides (NO, NO2)
Form when nitrogen and oxygen in the air react together at the very high temperatures created in a car engine
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Greenhouse effect
Greenhouse gases: absorb infra-red radiation from the earth's warm surface which would otherwise be radiated into space
–> traps heat energy in the atmosphere
Increased greenhouse gases => global warming => climate change
–> alterations in long-term weather patterns
–> melting polar ice caps, rising sea levels, more extreme weather