Atoms are smaller than molecules, and they are also the smallest building blocks of matter. Atoms make up molecules when two or more atoms bond.
The answer is to this question is c
I'm pretty sure it's A, but then again I'm only in 8th grade. Sorry if this doesn't help:(
Answer:
D. -120.9 kJ
Explanation:
According to Hess's law ,the total enthalpy change for a reaction is the sum of all changes regardless of the stages or the steps of the reaction.
....(1)

(this reaction should be reversed in order to reach the required reaction )
On reversing the reaction the sign of
get reversed.
(In this case change sign from '-' to'+'. Hence
= + 65 kJ)
....(1)
......(2)
Adding equation (1) and (2)
![Ca(OH)_{2} + 2HCl \rightarrow CaCl_{2} + 2H_{2}O[tex][tex]Delta H = - 186 + 65 = - 121\kJ](https://tex.z-dn.net/?f=%3Cstrong%3ECa%28OH%29_%7B2%7D%20%2B%202HCl%20%5Crightarrow%20CaCl_%7B2%7D%20%2B%202H_%7B2%7DO%3C%2Fstrong%3E%5Btex%5D%3C%2Fp%3E%3Cp%3E%5Btex%5D%3Cstrong%3EDelta%20H%20%3D%20-%20186%20%2B%2065%20%3D%20-%20121%5CkJ%3C%2Fstrong%3E)
(It is nearly equal to -120.9 kJ)