Definition of Diffusion – Friends of Reader, do you know about the process of diffusion? The process of diffusion can be found easily in everyday life. An example is when you dissolve sugar to make sweet tea or sprinkle salt into cooking. From the example we can understand that diffusion is the movement of a substance in a solvent from a high to a low concentration part.
Diffusion in the process involves two substances, one of which has a higher concentration than the other. This condition causes movement and mixing throughout the particles evenly. Diffusion is also said to be the flow or movement of a substance in a solvent from a high-concentration part to a low-concentration part. The difference in concentration between two solutions is called the concentration gradient.
To understand more, check out the following complete explanation of diffusion.
Definition of Diffusion
According to Britannica Encyclopedia , diffusion is a process resulting from the movement of molecules where the flow moves from an area of high concentration to an area of low concentration. According to the definition, the difference in concentration in two solutions is also known as the concentration gradient. Although there is no difference in concentration, molecular displacement can still occur to reach equilibrium.
The process of diffusion also occurs in the human body. Based on the explanation in the Class XI Biology Module compiled by Saifullah (2020), diffusion is the process of moving particles of a substance from a solution with a high concentration to a solution with a low concentration to achieve equilibrium.
An example of diffusion in the human body is when we breathe in, the alveoli expand and oxygen enters the lungs. Then, when exhaling, the alveoli deflate and carbon dioxide leaves the body. Well, this process occurs due to molecules moving from high to low concentration.
In general, diffusion is one of the mass transfer events that are often carried out in industries. The process of minimal diffusion involves two substances, one of the substances has a higher concentration than the other substance or it can be said that it is not in equilibrium, this situation can be the driving force of the diffusion process.
Diffusion will continue to occur until all particles are spread evenly or reach a state of equilibrium where the transfer of molecules still occurs even if there is no difference in concentration. A simple example is water vapor from a kettle diffusing in the air. Gradually the liquid becomes sweet. Another example is the addition of sugar to fresh tea liquid. The most common type of diffusion is molecular diffusion. Diffusion occurs when there is a displacement of a stationary layer of molecules from a solid or fluid.
In this experiment, what was studied was the liquid gas diffusion process and the liquid-liquid diffusion process. In this experiment, acetone liquid was used with temperature variation to find out its influence on the diffusion process. For liquefied gas diffusion, volatile liquids are used, so that the diffusion process is easy to see. In liquid-liquid diffusion, a solution is used that easily decomposes its ions in water, so that the diffusion process is easy to observe.
In this experiment, concentration variation was done to find out the influence on the diffusion process. This variation is done in order to obtain a comparison of the two variations as well as their influence on the diffusion coefficient.
Examples of diffusion in everyday life include:
- Freshwater fish placed in seawater causes the volume of the fish’s body to shrink because seawater is hypertonic to the body cells of living creatures. Consuming sea water causes the body to experience dehydration.
- The sprayed perfume will spread throughout the room due to diffusion with the air.
- Sugar that is added to a hot drink in a glass will spread throughout the volume of water in the glass even without stirring because it diffuses in the liquid.
Diffusion can occur in solids, liquids, or gases. In this case, the process does not require energy, which is why the diffusion process is also called a passive transport system. Diffusion process is a condition where the movement of substance particles with random movement that diffuses from the high concentration part towards the lower part through the cell membrane. A particle can pass through the membrane if the particle size is very small and can dissolve in water or fat.
Diffusion is a passive transport process. In the process of diffusion, the particles of a substance will move from an area of high concentration to an area with a lower concentration, so that it will produce the same concentration in the substance.
The diffusion process occurs as a result of the movement of a substance particle from an area of higher concentration to an area of lower concentration through a cell membrane. The condition for particles to be able to pass through the membrane during diffusion is that the size of the particles is very small and that the particles can dissolve in water and in fat.
Membrane permeability in the diffusion process is divided into:
1. Impermeable (Not Permeable)
Membrane that particles of dissolved substances and water cannot pass through. Example: membrane in rubber.
Membrane that particles of dissolved substances and water can pass through. Example: the cell membrane in a potato.
Membrane that cannot be passed by solute particles and only by water. Example: cell membrane in the cytoplasm.
Diffusion and Biology
In taking in important nutritional substances and removing unnecessary substances, cells perform various types of activities, and one of them is diffusion. There are two types of diffusion performed, namely normal diffusion and special diffusion.
Diffusion usually occurs when cells want to take in nutrients or molecules that are hydrophobic (non-polar or polar). Molecules can directly diffuse into the plasma membrane made of phospholipids . Diffusion like this does not require energy or ATP ( Adenosine Tri-Phosphate ).
Specific diffusion occurs when cells want to take in nutrients or molecules that are hydrophilic or polar and ions. Diffusion like this requires specific proteins that provide a path for the particles or help in the movement of the particles. This is done because the particles cannot pass through the plasma membrane easily. The proteins involved in this specific diffusion usually work for specific particles.
Factors Affecting Diffusion
The diffusion speed of a particle or molecule of a substance is influenced by several factors. The following are a number of factors that affect the diffusion process as follows:
1. Measurement of Diffused Molecules
If the molecule is large, the diffusion process will be slower to pass through the membrane than molecules with a smaller size.
Molecular movement will be faster when there is an increase in temperature. This of course has an impact on the rate of diffusion which is also getting faster. When the temperature gets higher, the particles will get more energy to move, so the diffusion speed gets bigger.
3. Substance Concentration
The rate of diffusion is also based on the large concentration gradient that exists in two substances.
4. Existence of Matter
The diffusion process in solids will usually be slower compared to liquids and gases. For example, the diffusion process of O 2 in single-celled animals. Diffusion can occur because the concentration of O 2 in the air is higher than the concentration of O 2 in the cell.
5. Membrane Thickness
The thinner the cell membrane, the greater the diffusion speed.
6. Area of an Area
The larger the area, the greater the diffusion speed.
The closer the distance between two concentrations, the greater the diffusion speed.
Types of Diffusion
Diffusion has two types, namely simple diffusion and assisted diffusion. Quoted from the Biology Module compiled by Saefullah (2020), the following is the explanation.
1. Medium Diffusion
In this type, diffusion is the movement of solid, liquid, or gaseous substances, whether they pass through the membrane or not, from a high-concentration (hypertonic) to a low-concentration (hypotonic) part. As a result of this displacement, the concentration of the substance becomes the same (isotonic). Cells want to take nutrition, or occur on hydrophobic (non-polar) molecules/particles. Particles will directly diffuse without needing energy, and can pass through the membrane directly.
2. Assisted Diffusion
This process occurs in cells that want to take nutrients, occurs in particles that have polar/ions ( hydrophilic ). This type of diffusion requires the help of specific proteins in the form of protein channels and transport proteins so that particles can pass through the membrane. For example in Escherichia coli bacteria which will decrease its metabolism if it is transferred into a lactose medium because it cannot pass through the cell membrane.
However, with the help of the permease enzyme, lactose can pass through the cell membrane. Permease enzymes are cell membrane proteins that pave the way for uncharged polar ions and molecules to pass through the hydrophobic lipid bilayer of the cell membrane.
Types of Diffusion
The diffusion process that we know is divided into three types, namely diffusion in liquid materials, diffusion in solid materials, and diffusion in gaseous materials. Here is the explanation.
1. Liquid Diffusion
It is said liquid diffusion if there is a movement of liquid molecules from a high concentration to a low concentration. An example is when we soak soybeans in water when making tempeh. During soaking, there will be diffusion of water from the outside environment (which has a high water content) into the soybeans (which has a low water content).
The tools needed in this practicum are a household balance that is used to weigh synthetic dyes (green terraces). A plastic spoon used to take the green terrace from the package into the paper as a base to weigh the green terrace. A 25 ml beaker that is used as a container for tap water and as a container for patio solution. A 50 ml measuring glass used to measure the volume of tap water. A series of heating tools consisting of a bunsen as a fire source, a tripod as a support, and a gauze as a beaker base when heated. A thermometer used to measure the temperature of heated tap water.
A stopwatch to calculate the length of time needed in the diffusion process until a homogeneous solution is formed. A glass funnel used to filter the green tea solution into a beaker. A dropper pipette used to take teres solution from beaker 1 put 5 ml of teres solution in another container. The materials used in this practicum are 50 ml tap water which is used as a solvent in the diffusion process. 5 ml of 30% green teres solution (made from 20 ml of tap water and 6 grams of green teres mixed until homogeneous). Lighter to light the flame on the bunsen. A filter paper that is used to help filter the green terrace solution to separate the precipitate.
2. Dense Diffusion
It is called solid diffusion if there is a movement of solid molecules from a high concentration to a low concentration. An example is when we soak fruit with a sugar solution in making fruit sweets. During soaking, in addition to the diffusion of water from the outside environment into the fruit, there is also the diffusion of sugar molecules (solid molecules) into the fruit and this means that diffusion of solids also occurs in the manufacture of this fruit candy. So far, the boundary between when water diffusion and solid diffusion occurs is still not clear because the processes often occur simultaneously and are difficult to distinguish.
The tools needed in this practicum are a household balance that is used to weigh synthetic dyes (green terrace). A plastic spoon that is used to take the green terrace from the packaging into the paper as a base to weigh the green terrace. A 25 ml beaker that is used as a container for tap water and as a container for patio solution. A 50 ml measuring glass used to measure the volume of tap water. A set of heating devices consisting of a bunsen as a fire source, a tripod as a support, and a gauze as a beaker base when heated. A thermometer used to measure the temperature of heated tap water.
A stopwatch to calculate the length of time needed in the diffusion process until a homogeneous solution is formed. A glass funnel used to filter the green tea solution into a beaker. A dropper pipette used to take teres solution from beaker 1 put 5ml of teres solution in another container. The materials used in this practicum are 20 ml tap water which is used as a solvent in the diffusion process. 6 grams of synthetic dye (teres green) is used as a solute in the diffusion process. Lighter to light the flame on the bunsen. A filter paper that is used to help filter the green terrace solution to separate the precipitate.
3. Gas Diffusion
It is said gas diffusion if there is a movement of gas molecules from a high concentration to a low concentration. An example is the diffusion of O 2 in plastic packaging. When we use plastic packaging to wrap a material, then during storage there will be diffusion of oxygen and water vapor from the outside environment into the packaging plastic.
The amount of oxygen and water vapor that can enter the packaging plastic varies depending on the permeability of the packaging plastic. The more amount of oxygen and water vapor that can get into the packaging plastic means that the quality of the packaging plastic is getting worse. Here, oxygen diffusion is gas diffusion and water vapor diffusion is liquid diffusion.
The greater the difference in concentration between the two regions, the sharper the gradation of concentration so that the speed of diffusion is slower. If the particles of a substance can move freely without being hindered by the force of attraction, then in a certain period of time the particles will spread evenly in the available space.
Until such an even distribution occurs, there will be more particles that move from areas where the particles are more concentrated to areas where the particles are less concentrated, then the opposite happens, and the overall movement of particles in a certain direction is called diffusion. The greater the difference in concentration between two areas, that is, the sharper the gradation of concentration, the greater the speed of diffusion (Diana, 2013).
The rate of diffusion can be increased by stirring so that equilibrium conditions can be reached more quickly. Another event that is also included as a diffusion event is blue ink that is dropped in clear water. The ink will diffuse slowly throughout the water until equilibrium conditions are obtained (no concentration gradient). To increase the rate of diffusion, stirring can be done, so that equilibrium conditions can be reached more quickly. Diffusion is not limited to the transfer of stagnant layers of solids or liquids.
In fluids that contain many components that will diffuse in a stationary state, Frick’s law applies for a mixture between laws A and B, namely:
J* AZ = molar flux of component A in the z-axis direction for molecular direction (kgmolA/cm 2 )
D AB = molecular diffusion of molecule A through B (m 2 /s)
z = diffusion distance (m)
c = concentration of A and B ( kgmol/m 3 )
x A = mole fraction of A from the mixture of A and B
If c is constant, because c A = cxA then:
cdxA = d(cxA) = dcA (2)
If equation (1) is substituted into equation (2) results in a diffusion equation for constant concentration:
Equation (3) is generally used in various applications of molecular diffusion processes. When the value of c varies, then the one used in equation (3) is the average value. For a turbulent mass flow with a constant concentration the equation applies:
with εM turbulent mass diffusivity with units of m 2 /s.
Well, that’s the meaning of diffusion along with influencing factors, types, and examples. Hope it’s useful!