Free Exothermic and Endothermic Reactions MCQs with Answers

• A. negative, because the products have less enthalpy than the reactants
• B. positive, because heat is released
• C. always zero
• D. negative, because the products have more enthalpy than the reactants

Explanation: Energy leaves the system as heat, so the products end up at a lower enthalpy and the difference, products minus reactants, is negative.

• A. Combustion of methane
• B. Photosynthesis
• C. Neutralisation of an acid by an alkali
• D. Condensation of steam

Explanation: Photosynthesis absorbs light energy to build glucose from carbon dioxide and water, so the products store more energy than the reactants…

• A. exothermic, since heat leaves the system
• B. at equilibrium
• C. endothermic, since heat is absorbed from the surroundings
• D. catalysed

Explanation: The system draws energy from its surroundings, and since the beaker and the solution are those surroundings their temperature falls.

• A. all acids contain the same number of hydrogen atoms
• B. the salts formed have similar masses
• C. the reaction is always carried out at the same concentration
• D. in every case the same reaction occurs, hydrogen ions combining with hydroxide ions to form water

Explanation: Strong acids and strong alkalis are fully ionised, so the spectator ions take no part and the only chemical change is the formation of…

• A. both exothermic
• B. both endothermic
• C. exothermic and endothermic
• D. endothermic and exothermic

Explanation: Energy must be supplied to pull bonded atoms apart, so breaking is endothermic, while forming a bond releases energy and is exothermic.

• A. the process is exothermic
• B. no energy change occurs
• C. the lattice energy is zero
• D. the energy absorbed in breaking the lattice exceeds the energy released on hydrating the ions

Explanation: Dissolving involves two steps with opposite signs: separating the ions from the lattice costs energy while surrounding them with water…

• A. products at a higher energy level than reactants, with an activation barrier in between
• B. products at a lower energy level than reactants
• C. no activation energy
• D. reactants and products at the same level

Explanation: In an endothermic reaction energy is absorbed overall, so the products lie above the reactants and the enthalpy change is positive, but…

• A. Endothermic
• B. Exothermic
• C. Thermally unstable
• D. Reversible

Explanation: The symbol in the original stem is the enthalpy change, which did not print cleanly in the paper.

• A. Endothermic
• B. Exothermic
• C. Fission
• D. Fusion

Explanation: Neutralization of an acid by a base usually releases heat because H+ ions combine with OH− ions to form stable water molecules, making the…

• A. Aerosol
• B. Ozone
• C. Acid rain
• D. PAN

Explanation: Acid rain contains sulfuric and nitric acids that lower soil pH and can damage soil organisms and nutrients, making it a cause of soil…

• A. 30 KJ
• B. 1 KJ
• C. 39 KJ
• D. 29 KJ

Explanation: Fat supplies approximately 39 kJ of energy per gram when metabolised, so 1 g fat releases about 39 kJ and option c is correct.

• A. Reaction is exothermic
• B. It is insoluble in water
• C. Dilute acid is produced
• D. All of above

Explanation: Sulphur trioxide reacts with water very vigorously and exothermically, producing a fine mist of sulphuric acid that is difficult to…

• A. Exothermic
• B. Moderate reaction
• C. No reaction

Explanation: If the reactants have more energy than the products, the energy difference is released to the surroundings as heat, making the reaction…

• A. dry zone burning zone decomposition zone cooling zone
• B. cooling zone burning zone decomposition zone dry zone
• C. burning zone cooling zone decomposition zone
• D. dry zone decomposition zone burning zone cooling zone

Explanation: In a rotary kiln, the material first loses moisture in the dry zone, then limestone decomposes in the decomposition zone, and finally the…

• A. roasted calcareous material
• B. roasted argillaceous material
• C. roasted calcareous and argillaceous material
• D. roasted gypsum

Explanation: Clinker forms when the calcareous material, mainly limestone, and argillaceous material, containing clay and silica, are heated together…

• A. vlay
• B. marine shells
• C. slate
• D. blast furnace slag

Explanation: Argillaceous materials are rich in silica and alumina and include clay, slate and some industrial slags.

• A. to dry the moisture of slurry
• B. to decompose lime stone to unslaked lime
• C. combination of different oxides like CaO SiO2 Fe2O3 and Al2O3
• D. to reduce the impurities

Explanation: The burning zone reaches a high enough temperature for CaO, SiO2, Al2O3 and Fe2O3 to react and form the clinker compounds of cement.

• A. 75% lime stone and 25% clay
• B. 25% lime stone and 75% clay
• C. 15% lime stone and 55% clay
• D. 55% lime stone and 15% clay

Explanation: The usual cement raw mix contains approximately 75% calcareous material, mainly limestone, and 25% argillaceous material, mainly clay.

• A. crushing heating mixing grinding
• B. crushing mixing heating grinding and mixing
• C. crushing grinding mixing heating
• D. mixing heating grinding crushing

Explanation: Cement manufacture proceeds by crushing the raw materials, grinding them, mixing the ground material to obtain a uniform composition, and…

• A. Lime (CaO)
• B. Silica (SiO2)
• C. Alumina (Al2O3)
• D. Magnesia (MgO)

Explanation: Calcium oxide is the major oxide in ordinary Portland cement because limestone is the largest part of the raw mix and decomposes to CaO on…