Consider the following double replacement reaction between silver nitrate and sodium chloride: AgNO_3(aq) + NaCl(aq) → AgCl(s) + NaNO_3(aq) \DeltaH^{\circ}_{rxn} Which of the following is the correct expression needed to calculate\DeltaH^{\circ}_{rxn}?

The question is not complete. Proposed completed question is:

When aqueous solutions of sodium chloride and silver nitrate are mixed, a double-displacement reaction occurs.  What is the balanced equation for the reaction?

               A.  

NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(aq)

               B.  

NaCl(aq) + AgNO3(aq) NaNO3(aq) + 3AgCl(s)

               C.  

NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(s)

               D.  

NaCl(aq) + AgNO3(aq) Na(s) + AgNO3Cl(aq)

               E.  

NaCl(aq) + AgNO3(aq) NaNO3(aq) + ClAg(s)

Answer is

       A.  

NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(aq)

Explanation:

Following the law of conservation of energy, the total number of atoms in the reactant  side is equal to the total number of atoms in the product side.

Proton and neutron

Explanation:

Electrons orbit round the nucleus as the planet revolve round the sun