from the site   http://www.thebigger.com/chemistry/thermodynamics/first-law-of-thermodynamics/derive-the-relation-between-cp-and-cv-in-gaseous-systems/

 Relation between C_P and C_V in gaseous systems 

 No external work is being done when a gas is heated at constant volume i.e. gas uses all the haet which is given to it for increasing itsinternal energy. Hence if temperature of one mole of a gas is raised through 1^oC, the molar heat capacity is given itself at constant volume by increase in internal energy. 

 But when a gas is heated at constant pressure there will be expansion of gas i.e. increase in volume take place and some external work will b done. For this some extra heat is required which should be given to the gas to perform the external work. 

 Hence the Molar Heat capacity of a gas at constant pressure must be greater than Molar Heat capacity of a gas at constant volume. 
 C_P > C_V

When gas is heated through 1^oC at constant pressure, the difference between these will give the work done by one mole of the gas in expansion. 

 As we know that at constant pressure work done by gas in expansion is given mathematically as: 

 w= P?V 
 For one mole of an ideal gas :
 PV = RT ……………………….. (1) 
 When temperature is raised by 1^oC from T to T + 1 so that volume becomes V + ?V, then 

 P (V + ?V) = R (T +1) ………………………………… (2) 

 Subtracting equation (1) from equation (2), we get: 
 P?V = R  

 Thus, At constant pressure work done by one mole of the an ideal gas in expansion when heated through 1^oC is equal to R. hence, 

 C_P – C_V = R 

 Thus, the difference between molar heat capacity of a gas at constant pressure, C_P and at constant volume, C_V is equal to the gas constant R. i.e. 1.987 cal or 8.314 J 

 ? means delta 

First select a no.

Write d multiples of it .

Go out of ur house try 2 match ur no. with d pbjects in d nature then go back 2 ur house

Pick up d calculator & Carry on the calculation.

 *************************************BEST OF LUCK**************