A 50-mL Mohr buret is connected to a 1-ft length of capillary tubing. The buret is then filled with water and the volume of water versus time is monitored as the water gradually flows through the capillary tubing.
This process is found to be first-order with a rate constant of 0.014 mL/sec. What will happen if the length of the capillary tube is doubled?
a)The process will still be first-order, but the rate constant will decrease.
b)The order and rate constant for the process will both change.
c)The order of the process will change, but the rate constant will be constant.
d)The process will still be first-order, but the rate constant will increase.
To answer the question, we need to understand the relationship between the length of the capillary tube and the rate constant for the process.
In a first-order process, the rate of the reaction is proportional to the concentration of the reactant. In this case, the concentration of water in the capillary tube is decreasing with time as it flows out of the buret.
When the length of the capillary tube is doubled, the flow of water through the capillary is expected to be slower, as there is now more distance for the water to travel. Intuitively, this means that it will take longer for the same volume of water to flow through.
This change in the flow rate does not affect the order of the process, as the reaction is still first-order with respect to the concentration of water. The order of the reaction refers to the power to which the concentration is raised in the rate equation, and that remains the same.
However, the rate constant is expected to change. The rate constant accounts for the specific reaction conditions, including the surface area, temperature, and any obstacles or resistance to the flow. In this case, doubling the length of the capillary tube increases the resistance to flow, which means that the rate constant will likely decrease.
Therefore, the correct answer is:
a) The process will still be first-order, but the rate constant will decrease.