Answer: C. Z is an intermediate.
Explanation: The given reaction is
And the rate equation is rate = k [X_2][Y]
From this, we can imply that either the concentration of Z is very small in comparison tot he other reactants or the reactant Z is an intermediate which is available only for the given small amount of time.
There can be various steps in the mechanism for the proposed reaction and Z can also react in any of the steps. It is not necessary that it should react in a step other than the rate determining step.
This might be possible that the activation energy for Z to react is very low But since it has made a new kind of product that is XZ, then the former cannot be true.
The correct answer would be a physical change
Answer:
Quantitative experiments show that 4.18 Joules of heat energy are required to raise the temperature of 1g of water by 1°C. Thus, a liter (1000g) of water that increased from 24 to 25°C has absorbed 4.18 J/g°C x 1000g x 1°C or 4180 Joules of energy.