Molecular Diffusion
ABSTRACT
A molecular diffusion experiment was conducted with the goal of determining the diffusion coefficient of acetone into air. For this experiment, acetone was placed in a capillary tube and was allowed to diffuse into non-diffusing air that was passed over the test tube at the temperature of 50oC.Thetemperature is kept constant and air stream is passed over the top of the tube to ensure that the partial pressure of the vapor is transferred from the surface of the liquid to be air stream bymolecular diffusion. The initial reading and every 2 minutes subsequent reading of the liquidacetone level are determined, and the experiment is conducted for 10 minutes. The experiment is repeated by changing temperature to 45oC and50oC. A graph of t/L-Loagainst L-Lois plotted and best fit of straight line and slope of the graph are obtained. The diffusivity of acetone at twodifferent temperatures is determined through calculation. The diffusivity of acetone at temperature of 40oC, 45oC and 50oCare 8.415 x 10-5 m2/s , 3.6006x 10-8 m2/s and 2.3980 x 10-8 m2/s respectively. Throughoutthe experiment, the diffusivity of acetone is determined to be higher at higher temperature.This fits the theory where temperature affects the diffusion rate. Several recommendation should be taken during operating this experiment to minimize the errors.
INTRODUCTION
Mass transport in a gas or liquid generally involves the flow of fluid (e.g. convection currents) although atoms also diffuse. Solids on the other hand, can support shear stresses and hence do not flow except by diffusion involving the jumping of atoms on a fixed network of sites. Diffusion can be divided into two types which are diffusion in a uniform concentration gradient and diffusion in a non-uniform concentration. Uniform concentration obeys Fick’s first law where the constant of proportionality is called the diffusion coefficient in m2s−1. Fick’s first law applies to steady state flux in a uniform concentration gradient. The diffusion
A molecular diffusion experiment was conducted with the goal of determining the diffusion coefficient of acetone into air. For this experiment, acetone was placed in a capillary tube and was allowed to diffuse into non-diffusing air that was passed over the test tube at the temperature of 50oC.Thetemperature is kept constant and air stream is passed over the top of the tube to ensure that the partial pressure of the vapor is transferred from the surface of the liquid to be air stream bymolecular diffusion. The initial reading and every 2 minutes subsequent reading of the liquidacetone level are determined, and the experiment is conducted for 10 minutes. The experiment is repeated by changing temperature to 45oC and50oC. A graph of t/L-Loagainst L-Lois plotted and best fit of straight line and slope of the graph are obtained. The diffusivity of acetone at twodifferent temperatures is determined through calculation. The diffusivity of acetone at temperature of 40oC, 45oC and 50oCare 8.415 x 10-5 m2/s , 3.6006x 10-8 m2/s and 2.3980 x 10-8 m2/s respectively. Throughoutthe experiment, the diffusivity of acetone is determined to be higher at higher temperature.This fits the theory where temperature affects the diffusion rate. Several recommendation should be taken during operating this experiment to minimize the errors.
INTRODUCTION
Mass transport in a gas or liquid generally involves the flow of fluid (e.g. convection currents) although atoms also diffuse. Solids on the other hand, can support shear stresses and hence do not flow except by diffusion involving the jumping of atoms on a fixed network of sites. Diffusion can be divided into two types which are diffusion in a uniform concentration gradient and diffusion in a non-uniform concentration. Uniform concentration obeys Fick’s first law where the constant of proportionality is called the diffusion coefficient in m2s−1. Fick’s first law applies to steady state flux in a uniform concentration gradient. The diffusion