(2)    Is the correct answer.

At STP, equal volumes of gases will have equal molecules.  In this case, 5 liters of two gases will contain the same the same number of molecules.

(3)    Is the correct answer.

Kinetic energy increases with temperature.  In this case, the volumes of the samples are relatively the same and both samples are in the same physical state; so, the sample at the highest temperature will have the highest kinetic energy.

(4)    Is the correct answer.  The dissolving of the LiBr(s) in water is an exothermic process.
As LiBr dissolves in water, heat is released (exothermic reaction) by the reaction so the reading on the thermometer initially increases.

(2) is the correct answer.  Oxygen gas behaves least like an ideal gas at low temperature and high pressure, when we begin to see a new phase of solid oxygen.

(1) is the correct answer:  The activation energy decreases.

A catalyst speeds up the rate of a reaction, or makes it occur more readily and at a faster rate.  To increase the rate of a reaction you need to increase the number of successful collisions. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy.

(2) Lower energy and more disorder is the correct answer.

Systems in nature will tend to lose energy to their surroundings and become more disordered (entropy increases).  Entropy is a measure of the lack of order in the energy. There is no definite value of entropy for a given system (as there is for, say, mass), as entropy is a purely statistical measure. When there is zero entropy, all the energy can be used. As the entropy increases, available energy decreases until, with maximum entropy, no useful energy is available.

(4) 72 g is the correct answer.

This problem is quite easy if you pay attention to the details.  No mass is lost in the equation, a complete reaction will produce:

First look at the products:

8g of H(2)= (8/(2x1) ) = 4 moles of H(2) (about)

64g of O2= 2 moles of O(2) (limiting reagent)

They react completely to form 2 moles of 2 H(2)O or (2x18x2) = 72 grams of H(2)O

(3) 65C is the correct answer.

65 C is the same as 338.15 kelvin (0C = 273 K).  As things tend to lose energy to their surroundings, when the water is hotter than the iron bar, the iron bar will take energy (or get hotter) when it is in water at a higher temperature.

(4) Energy is released as the bonds in CuS form.

This reaction is exothermic, which means that the bonding of the two elements results in a release of energy.   It is composed of a metal and a nonmetal, also known as an ionic bond.

(4) 7.5 mol is the correct answer.

In this combustion reaction, the ratio of the reactants is 1:5, which means that 1.5x5 or 7.5 mol of C3H8 are required to complete the reaction.