Answer:
The correct answer is:
<em>(1) It is important that the sample is dissolved in just enough hot solvent. </em>
Explanation:
The process of recrystallization is important to eliminate the impurities and to obtain better crystals of the solid. The solvent used to perform the recrystallization must have a high dissolution power of the substance to be recrystallized and a low dissolution power of the impurities. This is in order to eliminate most impurities. Furthermore, <em>It is important that the sample is dissolved in just enough hot solvent </em>because this should be easy to remove after the recrystallization and the crystal should form easily when the solution cools. Also, it is better to add the hot solvent to solubilize the crystals and keep the impurities insoluble, instead of adding the cold solvent and heating the solution. Additionally, the process of cooling the solution must be done slowly to obtain large and fewer crystals. A fast ice-cooling will form smaller crystals.
F and O
because they are more reactive than Cl
Answer:
The heat of formation = Heat of formation of the products - Heat of formation of the reactants
= -2323 + 104 = -2219 ≈ -2218.6 kJ/mol.
Explanation:
The law of conservation of energy states that the total energy is constant in any process. Energy may change in form or be transferred from one system to another, but the total remains the same
The heat of formation of C₃H₈ is 3C + 4 H₂ → C₃H₈ 
-104 kJ/mol
The heat of formation of O₂ is O₂ (g) → O₂ (g) 0 kJ/mol
The heat of formation of H₂O is H₂(g) + 1/2 O₂→ H₂O (g) -286kJ/mol
The heat of formation of CO₂ is C (s) + O₂ (g) → CO₂ (g) -393 kJ/mol
Therefore, in the given reaction we have;
C₃H₈ + 4 O₂ → 3 CO₂ + 4 H₂O
The heat of formation = Heat of formation of the products - Heat of formation of the reactants
The heat of formation = 3 × (-393) + 4 × (-286) - (-104) = -2219 ≈ -2218.6 kJ/mol.
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