Practice MCQ Questions and answers on Chemistry-GK

The heat value of combustion of Gasoline is 47000 kJ/kg.

The basic calorific value for solid and liquid fuels is the gross calorific value at constant volume and for gaseous fuels it is the gross calorific value at constant pressure. The calorific value in Kcal/Kg: Coal: 40007000; Natural gas: 8600; Coal gas: 4000; Water gas: 4600-4800; and LPG (liquefied petroleum gas such as Indane): 11,900 Kcal/Kg.

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The photon energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.

Relationship between K₁ and K₂ is K₁ = 1/K₂

The main reason that temperature increases the rate of reaction is that more of the colliding particles will have the necessary activation energy resulting in more successful collisions (when bonds are formed between reactants). The influence of temperature is described by the Arrhenius equation.

Sulphuric acid is used as a catalyst for refining and for producing alkylate, an essential component of high octane fuel. The hydrocarbon molecules are reformed into more complex molecules with a higher octane rating value.

Transition metals are used directly as catalysts in the anti–pollution catalytic converters in car exhausts. For example, expensive transition metals such as Platinum and rhodium are used in the catalytic converters in car exhausts to reduce the emission of carbon monoxide and nitrogen monoxide, which are converted to the non–polluting gases nitrogen and carbon dioxide. 2NO(g) + 2CO(g) ⇒ N₂(g) + 2CO₂(g)

Oxygen is colourless.

Iodine value can be used to measure the degree of unsaturation of oils and fats. The results are normally expressed as the number of grams of iodine absorbed by 100 g of oil or fat, considering the conditions of the test.

Helium (He) is an inert gas that is less narcotic than nitrogen at equivalent pressure (in fact there is no evidence for any narcosis from helium at all), so it is more suitable for deeper dives than nitrogen. Helium is equally able to cause decompression sickness.