Please help me with those questions.i need some people can check them with me?

Question

1.The rate of a chemical reaction is directly related to the number of collisions that occur between reactant molecules.True or False?

2. At equilibrium, all products and reactants coexist.True or False? it's true right?

3 at equilibrium the change in concentration over time for all reactants and products is zero. (Assume no changes in conditions such as temperature or pressure)

True or False ?it's false. i think so.

4.Water molecules are polar molecules (that is they have a dipole moment). This results in which of the following propertes of water?

Most ionic materials dissolve in water.

Water has a high boiling point.

or both of them are true,or neither?

5.Temperature does not change during a phase change.True or False?

Answer 1

1. True assuming that the collisions are at a high enough energy to overcome the activation energy and that the collisions are in the proper spatial orientation. The Arrhenius equation which gives the rate of a reaction shows that if you increase the collision frequency, you increase the rate of a reaction .

2. True, at equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction so both products and reactants coexist but usually not in equal amounts.

3. True, since the rate of the forward reaction is equal to the rate of the reverse, there is no change in the concentration of reactants or products. That doesn't mean that a reaction is not occurring, it just means that products are being formed from reactants at the same rate reactants are being formed from products, thus concentrations do no change.

4. Most ionic materials will dissolve in water but not all. Whether or not it dissolves has to do with thermodynamics and Gibbs free energy. But generally an ionic salt will dissolve in water.

Water has a very high boiling point due to high intermolecular attractions caused by hydrogen bonding. Hydrogen bonding decreases the vapor pressure of water. In order for boiling to occur, the vapor pressure of water must equal the atmospheric pressure. Strong hydrogen bonding in water keeps it's vapor pressure low and so generally when we heat water to boil it, we are increasing it's vapor pressure by increasing the internal kinetic energy of water which decreases it's ability to hydrogen bond.

5. True, during a phase change all energy put into a system goes strictly into breaking hydrogen bonds.