Question

(a) What are the units usually used to express the rates of reactions occurring in solution? (b) From your everyday experience, give two examples of the effects of temperature on the rates of reactions. (c) What is the difference between average rate and instantaneous rate?

Short answer

(a) For reactions in solution, the units typically used to express reaction rates are molarity/time (M/s or M/min). (b) Two examples of the effects of temperature on reaction rates are: 1) Food spoilage occurs faster at higher temperatures due to increased decay processes, 2) Ice melts faster at higher temperatures as the transition rate from a solid to liquid state increases. (c) The difference between average and instantaneous rates is that average rate represents the total change in concentration over a time interval, while instantaneous rate represents the rate of a reaction at an exact moment in time (mathematically, the derivative of the concentration with respect to time).

Step-by-step solution

(a) Units of reaction rates

Reaction rates describe the speed at which reactants are converted into products. For reactions occurring in solution, the units often used are molarity per unit time (M/s or M/min). Molarity (M) is the concentration of a solute in moles per liter (mol/L).

(b) Effects of temperature on the rates of reactions

Temperature has a substantial effect on reaction rates. Generally, the rate of a reaction increases with increasing temperature. This is because the particles in the reaction have more energy and thus collide more effectively, resulting in a higher reaction rate. Example 1: Food spoilage. At higher temperatures, food spoils more rapidly due to the increased reaction rate of the processes that cause decay, such as bacterial growth and enzyme activity. Example 2: Ice melting. The melting of ice is a physical process where water molecules transition from a solid state to liquid state. As we increase the temperature, the rate of this transition increases, causing the ice to melt faster.

(c) Average rate vs. instantaneous rate

Average rate and instantaneous rate are two ways to describe the speed of a reaction at different timescales. Average rate: The average rate is the total change in the concentration of a reactant or product over a specific time interval. It is calculated by dividing the change in concentration by the change in time during that interval. Average rate gives an overview of the speed of the reaction over a particular period, but it doesn't provide information about the exact rate at any specific point in time. Instantaneous rate: The instantaneous rate is the rate of a reaction at an exact moment in time. It can be thought of as the limiting value of the average rate as the time interval approaches zero. In mathematical terms, it is the derivative of the concentration with respect to time. Instantaneous rates give a more detailed view of the reaction's progress, but are more difficult to determine experimentally.