What is the number of formula units in a 9.87 mol sample of NH4NO3 ?
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Answer:
- Question 19: the three are molecular compounds.
- Question 20: CuSO₄.5H₂O
Explanation:
<em>Question 19.</em>
- C₂H₄
- HF
- H₂O₂
All of them are the combination of two kinds of different atoms in fixed proportions.
- C₂H₄: two carbon atoms per four hydrogen atoms
- HF: one hydrogen atom per one fluorine atom
- H₂O₂: two hydrogen atoms per two oxygent atoms
Thus, they all meet the definition of compund: a pure substance formed by two or more different elements with a definite composition.
Molecular compounds are formed by covalent bonds and ionic compounds are formed by ionic bonds.
Two non-metal elements, like H-F, C - C, C - H, H-O, H - H, and O - O will share electrons forming covalent bonds to complete their valence shell. Thus, the three compounds are molecular and not ionic.
<em>Question 20. </em>Formula of copper(II) sulfate hydrate with 36.0% water.
Copper(II) sulfate is CuSO₄. Its molar mass is 159.609g/mol
Water is H₂O. Its molar mass is 18.015g/mol
Calling x the number of water molecules in the hydrate, the percentage of water is:
From which we can solve for x:
Thus, there are 5 molecules of water per each unit of CuSO₄, and the formula is:
- CuSO₄.5H₂O
Given information : H = -92 KJ/mol and S = -0.199 KJ/(mol.K)
At equilibrium G = 0
We have to find the Temperature at which reaction would be spontaneous.
For spontaneous reaction :
For non-spontaneous reaction :
We can find the temperature using the formula for Gibbs free energy which is:
Where, G = Gibbs free energy ,
H = Enthalpy
S = Entropy
T = Temperature
By plugging the value of G , H and S in the above formula we can find 'T'
Since reaction should be spontaneous that means should be negative , so the above formula can be written as :
On rearranging the above formula we get :
For the reaction to be spontaneous , T should be less than 462.3 K, so out of given option , C is correct which is 400 K.