Test: Enthalpy - NEET MCQ

The symbol represents enthalpy of combustion which is always exothermic. For exothermic rxn delta H is always -ve. 

Enthalpy is a state function; which means change in enthalpy depends only on final and initial state. So, the change in enthalpy for a cyclic process is zero.

Due to high lattice enthalpy of fluorides, it is difficult to break the lattice of fluoride compounds(due to the small size of fluorine, so the lattice is strong). SO the solubility of fluorides is less than chlorides.

Enthalpy of solution (ΔHsoln) is the change in enthalpy that occurs when a specified amount of solute dissolves in a given quantity of solvent.

The interparticle forces are strongest in NH₃ (Hydrogen bonding). In PH₃ and AsH₃ the inter-particle forces are dipole-dipole forces which are relatively stronger in AsH₃(due to higher mass of AsH₃). So the increasing order of vaporization is PH₃<AsH₃<NH₃ .

The Born-Haber cycle is based on Hess Law or Law of constant heat summation. It states that the standard enthalpy of reaction is the sum of algebraic sum of the standard enthalpies of reactions into which the overall reaction may be splitted. So the change in enthalpy around a cycle is zero.

The enthalpies of fusion for all reactions are always positive because melting of a solid is an endothermic process in which heat is supplied to the reaction Hence the sum of enthalpies of the product is greater than the sum of enthalpies of the reactant.

∆H_r is called both enthalpy of combustion of hydrogen as well as enthalpy of formation of water.For the enthalpy of combustion of hydrogen, the reason is that 1 mole of Hydrogen is burnt in its pure state. For the formation of water, the reason is that 1 mole of water is formed from its constituent elements.

When an ionic compound is dissolved in the solvent, the compound dissociate into ions and due to external medium i. e. solvent it leave its original position in crystal lattice n gets hydrated..
Eg. NaCl(aq) → Na+(aq) + Cl-(aq)