Answer:
Explanation:
13 ) symbol of enthalpy change = Δ H .
14 ) enthalpy change is nothing but heat absorbed or evolved .
During fusion enthalpy change
Δ H .= m Lf , m is mass and Ls is latent heat of fusion
During evaporation, enthalpy change
Δ H .= m Lv , m is mass and Lv is latent heat of evaporation
during temperature rise , enthalpy change
Δ H = m c Δ T
In case of gas , enthalpy change can be calculated by the following relation
Δ H = Δ E + W , Δ E is change in internal energy , W is work done by gas.
15 ) When enthalpy change is negative , that means heat is released to the environment .So reaction is called exothermic .
when heat is absorbed enthalpy change is positive . Reaction is endothermic.
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Answer:
The number of atoms present in one unit of the following compounds is:
a). Potassium Iodide , KI = 2
b).Sodium Sulfide, 
= 3
c). Silicon Dioxide , 
= 3
d). Carbonic Acid ,
= 6
Explanation:
Atomicity : It is defined as the number of atoms that are present in a given molecule/compound.
Atom : The smallest unit of matter is called atom. For e.g O is atom of oxygen but 
is not an atom , it is molecule of oxygen .
molecule has 2 atoms of Oxygen
Similarly Na , K , Fe are atoms but ,
,
,
are molecules
a).Potassium Iodide
KI = 1 atom of K + 1 atom of I
Total atoms = 2
b) Sodium Sulfide
= 2 atoms of Na + 1 atom of S
Total atoms = 3
c) Silicon Dioxide
= 1 atom of Si + 2 atoms of O
Total atoms = 3
d) Carbonic Acid
= 2 atom of H + 1 atom of C + 3 atom of O
= 2+1+3
Total atoms = 6
