Choose the substance with the lowest vapor pressure at a given temperature.

(a) bf3
(b) pf5
(c) becl2
(d) he
(e) co2

C

Explanation:

The vapor pressure is the pressure that the vapor does when it is in equilibrium with the liquid that originated it. So, it's a measure of the tendency of the boil of the liquid, and as higher is the vapor pressure, more easily will be to the liquid to boils, so lower will be the boiling point.

The boiling point depends on the strength of the intermolecular force of the substance and the molar mass of the substance. As higher is them, as higher is the boiling point.

BF3 is a nonpolar covalent compound, so it has London forces, which are the weakest. It has 67.82 g/mol of molar mass.

PF5 is also a nonpolar covalent compound and has London forces. Its molecular mass is 126 g/mol.

BeCl2 is an ionic compound formed by the ions Be+2 and Cl-, and the ionic force (ion-ion) is the strongest. Its molar mass is 80 g/mol.

He is a noble has, and so, has a weak force between its atoms. Its molar mass is 4 g/mol.

CO2 is a nonpolar compound, so it has London forces too. It has a molar mass of 44 g/mol.

So, the compound of the strong molar force is BeCl2, and at room temperature, it is solid (all ionic compounds are solid at room temperature). All the other compounds are gases at room temperature, so BeCl2 has the highest boiling point, and because of that, the lowest vapor pressure.

hurricanes form in warm water

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.