Preston's clock produces 45 useful energy units for every 100 units of electricity used. What is the efficiency of the clock?

Iron (3) oxide will decompose in the presence of hydrogen gas and heater to produced iron and digydrogen monoxide white a balanced chemical equation

What mass of natural gas (ch4) must you burn to emit 276 kj of heat?

Oil rich countries in the middle east cover about 4% of earths total land area but prossess about 48% of the worlds known oil reserves what is the main reason for high concentration of reserves in this part of the world