When the particles from a liquid spread out and form a gas it is called?

The liquid state of matter is an intermediate phase between solid and gas. Like the particles of a solid, particles in a liquid are subject to intermolecular attraction; however, liquid particles have more space between them, so they are not fixed in position. The attraction between the particles in a liquid keeps the volume of the liquid constant. 

The movement of the particles causes the liquid to be variable in shape. Liquids will flow and fill the lowest portion of a container, taking on the shape of the container but not changing in volume. The limited amount of space between particles means that liquids have only very limited compressibility. 

Cohesion and adhesion

Cohesion is the tendency for the same kind of particles to be attracted to one another. This cohesive "stickiness" accounts for the surface tension of a liquid. Surface tension can be thought of as a very thin "skin" of particles that are more strongly attracted to each other than they are to the particles surrounding them. As long as these forces of attraction are undisturbed, they can be surprisingly strong. For example, the surface tension of water is great enough to support the weight of an insect such as a water skipper. Water is the most cohesive nonmetallic liquid, according to the U.S. Geological Survey.

Cohesive forces are greatest beneath the surface of the liquid, where the particles are attracted to each other on all sides. Particles at the surface are more strongly attracted to the identical particles within the liquid than they are to the surrounding air. This accounts for the tendency of liquids to form spheres, the shape with the least amount of surface area. When these liquid spheres are distorted by gravity, they form the classic raindrop shape.

Adhesion is when forces of attraction exist between different types of particles. Particles of a liquid will not only be attracted to one another, but they are generally attracted to the particles that make up the container holding the liquid. Particles of the liquid are drawn up above the surface level of the liquid at the edges where they are in contact with the sides of the container. 

The combination of cohesive and adhesive forces means that a slight concave curve, known as the meniscus, exists at the surface of most liquids. The most accurate measurement of the volume of a liquid in a graduated cylinder will be observed by looking at the volume marks closest to the bottom of this meniscus. 

Adhesion also accounts for capillary action when a liquid is drawn up into a very narrow tube. One example of capillary action is when someone collects a sample of blood by touching a tiny glass tube to the blood droplet on the tip of a pricked finger.

Viscosity

Viscosity is a measure of how much a liquid resists flowing freely. A liquid that flows very slowly is said to be more viscous than a liquid that flows easily and quickly. A substance with low viscosity is considered to be thinner than a substance with higher viscosity, which is usually thought of as being thicker. For example, honey is more viscous than water. Honey is thicker than water and flows more slowly. Viscosity can usually be reduced by heating the liquid. When heated, the particles of the liquid move faster, allowing the liquid to flow more easily.

Evaporation 

Because the particles of a liquid are in constant motion, they will collide with one another, and with the sides of the container. Such collisions transfer energy from one particle to another. When enough energy is transferred to a particle at the surface of the liquid, it will eventually overcome the surface tension holding it to the rest of the liquid. Evaporation occurs when surface particles gain enough kinetic energy to escape the system. As the faster particles escape, the remaining particles have lower average kinetic energy, and the temperature of the liquid cools. This phenomenon is known as evaporative cooling.

Volatility

Volatility can be thought of as how likely a substance will be to vaporize at normal temperatures. Volatility is more often a property of liquids, but some highly volatile solids may sublime at normal room temperature. Sublimation happens when a substance passes directly from solid to gas without passing through the liquid state. 

When a liquid evaporates inside a closed container, the particles cannot escape the system. Some of the evaporated particles will eventually come into contact with the remaining liquid and lose enough of their energy to condense back into the liquid. When the rate of evaporation and the rate of condensation are the same, there will be no net decrease in the amount of liquid. 

The pressure exerted by the vapor/liquid equilibrium in the closed container is called the vapor pressure. Increasing the temperature of the closed system will increase the vapor pressure, according to Purdue University's department of chemistry. Substances with high vapor pressures can form a high concentration of gas particles above the liquid in a closed system. This can be a fire hazard if the vapor is flammable. Any small spark, even one occurring from the friction between the gas particles themselves, can be enough to cause a catastrophic fire or even an explosion. The U.S. Occupational Safety and Health Administration (OSHA) requires Material Safety and Data Sheets to give information about the volatility and flammability of liquids in order to help prevent accidents from occurring.

Further reading

Water is the only common substance that is naturally found as a solid, liquid or gas. Solids, liquids and gases are known as states of matter. Before we look at why things are called solids, liquids or gases, we need to know more about matter.

Matter is everything around us

Matter can be a confusing word because it has several meanings. We often hear phrases like “What is the matter?” or “It doesn’t matter”. Scientists have a different meaning for matter – matter is anything that occupies space and has mass.

Matter is made up of tiny particles. These can be atoms or groups of atoms called molecules. Atoms are like individual LEGO blocks. They are the smallest unit that anything can be broken down into without doing something extreme (like hitting a LEGO block with a hammer or smashing atoms in the Large Hadron Collider.) If atoms are like LEGO blocks, molecules are the structures you build with them. The physical characteristics of atoms and molecules decide the form or state the matter is in.

Solid

Right now, you are probably sitting on a chair, using a mouse or a keyboard that is resting on a desk – all these things are solids. Something is usually described as a solid if it can hold its own shape and is hard to compress (squash). The particles in most solids are closely packed together. Even though the particles are locked into place and cannot move or slide past each other, they still vibrate a tiny bit.

Ice is water in its solid form or state. Ice keeps its shape when frozen, even if it is removed from its container. However, ice is different from most solids: its molecules are less densely packed than in liquid water. This is why ice floats.

Liquid

The simplest way to determine if something is a liquid is to ask this question: If I try and move it from one container to another (i.e. by pouring), will it conform to (take on the shape of) the new container?

If you have a glass of water and pour it into another glass, it clearly conforms – it takes on the shape of the glass. If you spill the water, it will go everywhere. Because it isn’t in a container, it conforms to the shape of the floor, making a big puddle!

In most liquids, the particles are less densely packed, giving them the ability to move around and slide past each other. While a liquid is easier to compress than a solid, it is still quite difficult – imagine trying to compress water in a confined container!

Water is an example of a liquid, and so are milk, juice and lemonade.

Find out more about water by looking at our wide range of resources under the water topic.

Gas

The atoms and molecules in gases are much more spread out than in solids or liquids. They vibrate and move freely at high speeds. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid. (Think about a diving tank – 600 L of gas is compressed into a 3 L cylinder.) Right now, you are breathing in air – a mixture of gases containing many elements such as oxygen and nitrogen.

Water vapour is the gaseous form or state of water. Unlike ice or water, water vapour is invisible. We exhale water vapour whenever we breathe out. We cannot see the water vapour as we exhale, but if we hold our eyeglasses or smartphone to our mouths, we can see the water vapour condensing (becoming liquid) on these objects.

Other states of matter

We’ve known about solids, liquids and gases for hundreds of years, but scientists have discovered other states. One state is plasma, which naturally occurs in lightning, and we create it in fluorescent light bulbs and plasma TVs. Another state of matter is Bose-Einstein condensate, but this state only occurs with super-low temperatures.

Science knowledge changes as we discover new evidence. Technology helps us find this evidence. For example, it wasn’t until 1995 that scientists had the equipment and facilities to create Bose-Einstein condensate.