The graph shows the change in concentration of one of the species in the reaction ab --> a + b + heat. if the graph indicates the reaction rate, then the concentration of which species is plotted?
a

ab

b

The concentration of AB is being plotted in the graph.

Explanation:

In a chemical reaction, products are formed in a course of time from the reactants.

As, the time of the reaction proceeds, the reactants form products, which means that the concentration of the reactants decreases as the reaction proceeds in the forward direction. While, the concentration of products increase as the reaction proceeds.

Reactants are written on the left side and products are written on the right side.

From the given graph, concentration of the species is decreasing as the time increases. Thus, the specie is a reactant which is AB.

Thus, the concentration of AB is being plotted in the graph.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements