Question

With increase in temperature the surface tension and viscosity coefficient of a liquid (1) increases for both (2) decreases for both (3) surface tension decreases while viscosity coefficient increases (4) surface tension increases while viscosity coefficient decreases

Short answer

The correct answer is (2) decreases for both.

Step-by-step solution

- Understanding surface tension

Surface tension is the energy required to increase the surface area of a liquid. It generally decreases with an increase in temperature because the increased molecular activity reduces the cohesive forces between molecules.

- Understanding viscosity coefficient

Viscosity is the measure of a fluid's resistance to flow. The viscosity coefficient of a liquid typically decreases with an increase in temperature because the fluid molecules can move more freely at higher temperatures, reducing internal friction.

- Evaluating the options

By examining the effects of temperature on both surface tension and viscosity coefficient, it is clear that both properties decrease as temperature increases.

- Choosing the correct answer

Based on the explanation, the correct option is (2) decreases for both.

Key concepts

surface tension

Surface tension refers to the energy required to increase the surface area of a liquid, resulting from the cohesive forces between liquid molecules. These forces make it as if the liquid's surface is covered with an invisible film.
When we heat a liquid, the molecules move faster. This increased molecular movement reduces the strength of these cohesive forces, leading to a decrease in surface tension.
For example, when you heat water, it is easier for bubbles to form because the surface tension is lower. These concepts are crucial in understanding the behavior of liquids under different temperatures.

viscosity coefficient

The viscosity coefficient is a measure that describes a fluid's resistance to flow. In simpler terms, it tells us how 'thick' or 'thin' a liquid is. Honey, for instance, has a higher viscosity than water, meaning it flows more slowly.
As the temperature of a liquid increases, the viscosity typically decreases. This happens because the increased thermal energy allows the molecules to overcome the internal friction more easily, letting them slide past each other with less resistance.
A practical example of this is motor oil, which becomes thinner (less viscous) when the engine heats up, allowing it to flow more freely and lubricate engine parts efficiently.

temperature increase

Temperature can significantly affect the properties of liquids, including surface tension and viscosity.
When the temperature increases, kinetic energy of the liquid molecules also increases. This results in:

• Reduced surface tension, making it easier for the liquid to spread out and form bubbles or droplets.
• Decreased viscosity, allowing the liquid to flow more easily and reducing its resistance to motion.

This behavior is crucial for many practical applications, such as in industrial processes where precise liquid handling is required, or in everyday situations like cooking, where the consistency of ingredients can change with temperature.