Viscosity

Viscosity

What is it?

Viscosity is a liquid's resistance to flowing smoothly due to forces holding the molecules together. Viscosity increases as temperature decreases.

Give me an example!

Have you ever heard someone say that something is "slower than molasses in January"? That refers to viscosity. In other words, when it's cold (like in January), molasses doesn't flow as readily as it does during warmer months (like July).

Capillary Action

Capillary Action

What is it?

Capillary action is the movement of water or any other liquid through a thin tube. The speed and distance with which capillary action moves a liquid depends on how much resistance the liquid encounters due to pressure against it inside the tube.

Give me an example!

Did you ever wonder how water gets from deep in the earth to the leaves of trees hundreds of feet above the ground? It's all because of capillary action! Water moves through fine pores in soil and rises through tiny tubes and vessels inside the roots, trunk, and branches of the tree all the way to the leaves. There it nourishes the tree and helps it make its own food in a complicated chemical reaction called photosynthesis.

Density

Density

What is it?

Density is a property of a substance that can be measured, and every substance has a different density. Density is the mass of the substance divided by the volume occupied by the substance.

Density is expressed in terms of units of mass per units of volume, such as grams per mililitre or pounds per square inch.

Give me an example!

Have you ever held a piece of lead in your hand? Did it feel really heavy for its size? That's because lead has a very high density compared to most substances. In other words, a specific volume of lead has a greater mass than a that same volume of another substance (say, salt).

Condensation

Condensation

What is it?

Condensation is when a gas turns into a liquid. This is done by cooling the gas. Condensation is the opposite of evaporation.

Give me an example!

Have you ever seen how car windows fog up on a cold day? That's an example of condensation. The water vapor in your breath is a gas, and as it comes from inside your warm body, it condenses into droplets of liquid on the cold inside surface of the car windows. If it's cold enough, that liquid will freeze on the window and become frost.

Evaporation

Evaporation

What is it?

Evaporation is when a liquid becomes a gas. This is usually done by heating the liquid. Evaporation is the opposite of condensation.

Give me an example!

Have you ever watched steam rise from a pot of boiling water? The water in the pot is a liquid -- and as it is heated, it begins to evaporate and become steam, which is a gas.

Heat of Vaporization

Heat of Vaporization

What is it?

Heat of Vaporization is the change in enthalpy (or heat) needed to cause the evaporation one mole of a liquid.

Give me an example!

When a substance reaches its heat of vaporization, the bonds between the molecules that hold it together in a liquid state break down and it becomes a gas. You might say the bonds between the molecules vaporize when the substance reaches its heat of vaporization.

Enthalpy

What is it?
Enthalpy is the heat content of a substance. The change in enthalpy in a reaction is the difference between the heat contained in the products and the heat contained in the reactants.

In an endothermic reaction, heat is absorbed, which would create a positive enthalpy. In an exothermic reaction, heat is given off, which means the reaction would have a negative enthalpy.

Give me an example!

Have you ever made ice? Then you have lowered the enthalpy of water! Have you ever melted ice? Then you have raised the enthalpy of water!