Question

1. Define the term standard state.

2. Distinguish between an endothermic and an exothermic process.

3. Write the thermochemical equation for the standard enthalpy of fusion of He at 3.5 K. Be sure to give the physical state for all reactants and products in the chemical equation and use the appropriate, complete symbol for the enthalpy change, including units.

4. Consider the first (Ei1) and second (Ei2) standard enthalpy of ionization values for Na and Mg given in Table 2E.2 in the textbook. Why is Ei2/ Ei1 so much larger for Na (≈ 9) than for Mg (≈ 2)?

5. Why is the standard electron gain enthalpy for I negative but that for Sr is positive?

Answer 1

1- In physical chemistry, for the purpose of easy calculation, we take the concept of Standard State- which is state of a material (may be a pure substance,a mixture or a solution) taken as a reference point - used to calculate its properties under different conditions.

It can be any physical property- such as temp, pressure in any unit of the comfort of the user.

Generally this satandard state is used to determine the material's thermodynamic state properties such as- enthalpy, entropy, Gibbs free energy etc. And the caclulated property at this state is mentioned as Stanard enthlpy, standard gibbs free energy etc.

2- The term Endo means- inside and Exo means- outside, Thermic means- Temp,

Hence Endothermic Process- means- The process in which energy is consumed.

i.e In Endothermic Reaction Energy of the product is less than energy of reactant. Here the delH (change in enthalpy) is -ve. Physically if we touch a beaker in which an endothermic reaction has taken place, the wall of the beaker will be felt colder.

On the otherhand, In Exothermic Process, energy is released to outside. In exothermic recations, the energy of product is more than energy of reactant. Here the delH will be +ve.

9 2 24 2

4- Electron gain enthalpy of an element is the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative Ion i.e. anion.