Final answer:
The term "reaction rate" most closely relates to the speed of a reaction, reflecting how quickly reactants are converted into products. It is particularly dependent on the number of collisions per second and the temperature which can increase the rate of a reaction by elevating the energy of the molecules involved.
Step-by-step explanation:
The term most closely related to reaction rate is c. the speed of a reaction. This is because reaction rate refers to how quickly a chemical reaction occurs, or in other words, the speed at which reactants are converted into products. In the context of collision theory, the rate of a chemical reaction is proportional to the number of collisions per second (option c), where more frequent collisions between reactant molecules typically result in a higher reaction rate. Reaction rates can be affected by several factors, including reactant concentrations and temperature.
In the case of hydrogen iodide (HI) decomposition, the rate constant, k, varies with temperature, indicating that reaction rates are temperature-dependent. As temperature increases, so does the rate constant, leading to a faster reaction rate. This is because a higher temperature typically increases the energy of the molecules involved, leading to more collisions with sufficient energy to overcome the activation barrier, and hence a higher reaction rate.
When considering a change in concentration affecting a reaction in equilibrium, the shift in rates of the forward or reverse reactions can cause the position of equilibrium to change. However, the position of equilibrium itself (option b in the initial question) is not the same as reaction rate. Similarly, the temperature needed to initiate a reaction (option a) influences reaction rate, but it is not itself the rate.