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Physics: Energy, Climate, and Sustainability - Fossil Fuels and their Environmental Impacts

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Fossil fuels (coal, oil, and natural gas) are non-renewable energy sources formed from the remains of ancient plants and animals buried under high pressure and heat over millions of years.

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Combustion is the chemical process of burning fossil fuels to release energy. The general equation for hydrocarbon combustion is: Fuel+O2→CO2+H2O+EnergyFuel + O_{2} \rightarrow CO_{2} + H_{2}O + Energy

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Energy Density is the amount of energy stored per unit volume of fuel (measured in J/m3J/m^3), while Specific Energy is the energy stored per unit mass (measured in J/kgJ/kg).

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Efficiency (η\eta) describes the ratio of useful energy output to the total energy input. No energy transformation is 100%100\% efficient due to energy 'losses' as thermal energy (heat).

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The Greenhouse Effect: Greenhouse gases like carbon dioxide (CO2CO_{2}) and methane (CH4CH_{4}) absorb infrared radiation emitted by the Earth, trapping heat in the atmosphere and causing global warming.

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Environmental Impacts: Combustion releases pollutants such as sulfur dioxide (SO2SO_{2}) and nitrogen oxides (NOxNO_{x}), which react with water vapor to form acid rain: SO2+H2O→H2SO3SO_{2} + H_{2}O \rightarrow H_{2}SO_{3} (Sulfurous acid).

📐Formulae

η=EusefulEtotal×100%\eta = \frac{E_{useful}}{E_{total}} \times 100\%

Specific Energy=EnergyMassSpecific\ Energy = \frac{Energy}{Mass}

Energy Density=EnergyVolumeEnergy\ Density = \frac{Energy}{Volume}

Etotal=Euseful+EwasteE_{total} = E_{useful} + E_{waste}

💡Examples

Problem 1:

A coal-fired power station consumes 80,000,000 J80,000,000\text{ J} of chemical potential energy. If the useful electrical energy produced is 28,000,000 J28,000,000\text{ J}, calculate the efficiency of the station and the amount of energy wasted as heat.

Solution:

  1. To find the wasted energy: Ewaste=Etotal−EusefulE_{waste} = E_{total} - E_{useful} 80000000−2800000052000000\begin{array}{r} 80000000 \\ -28000000 \\ \hline 52000000 \end{array} 2. To find efficiency: η=28,000,00080,000,000×100=35%\eta = \frac{28,000,000}{80,000,000} \times 100 = 35\%

Explanation:

The power station converts chemical energy into electrical energy. The difference between the input and useful output is the energy dissipated to the surroundings, usually as heat. The efficiency of 35%35\% means only about one-third of the energy in the coal is actually converted into electricity.

Problem 2:

If the specific energy of a certain type of coal is 30 MJ/kg30\text{ MJ/kg}, how much energy is released by burning 5 kg5\text{ kg} of this coal?

Solution:

Energy=Specific Energy×MassEnergy = Specific\ Energy \times Mass Energy=30 MJ/kg×5 kg=150 MJEnergy = 30\text{ MJ/kg} \times 5\text{ kg} = 150\text{ MJ}

Explanation:

Specific energy tells us the energy content per unit of mass. By multiplying the mass of the fuel by its specific energy, we find the total energy available for release during combustion.