Which phases are exothermic

When you're going from particles that are in a higher energy state to particles that are in a lower energy state, you must take away energy. This implies that the process will be exothermic , since heat is being released.

You will thus have. And there you have it -- six phase changes, three exothermic and three endothermic, correspond to the three traditional phases of matter , liquid, solid, and gas. For the three states of matter solid, liquid, and gas there are six possible changes of state. Which changes of state are exothermic and which are endothermic?

Chemistry Matter Phases of Matter. The release of energy is felt as heat as the water vapor goes to water. A good way to remember all of these is that opposite phase changes have opposite energy needs.

If you know that from solid to liquid to gas requires the addition of heat endothermic , that means you know that going from gas to liquid to solid requires the removal of heat exothermic. When going from a more ordered state to a less ordered state, the process is exothermic. When going from a less ordered state to more ordered state, the process is endothermic.

She has an interest in astrobiology and manned spaceflight. She has over 10 years of biology research experience in academia. She currently teaches classes in biochemistry, biology, biophysics, astrobiology, as well as high school AP Biology and Chemistry test prep. Here is how to classify the phase changes as endothermic or exothermic:. Endothermic Science Projects. Explaining Why Condensation Is Exothermic.

Conversely, any transition from a less ordered to a more ordered state liquid to solid, gas to liquid, or gas to solid releases energy; it is exothermic.

Previously, we defined the enthalpy changes associated with various chemical and physical processes. The substances with the highest melting points usually have the highest enthalpies of fusion; they tend to be ionic compounds that are held together by very strong electrostatic interactions. Substances with high boiling points are those with strong intermolecular interactions that must be overcome to convert a liquid to a gas, resulting in high enthalpies of vaporization.

The enthalpy of vaporization of a given substance is much greater than its enthalpy of fusion because it takes more energy to completely separate molecules conversion from a liquid to a gas than to enable them only to move past one another freely conversion from a solid to a liquid. Less energy is needed to allow molecules to move past each other than to separate them totally.

The direct conversion of a solid to a gas, without an intervening liquid phase, is called sublimation. Fusion, vaporization, and sublimation are endothermic processes; they occur only with the absorption of heat. Anyone who has ever stepped out of a swimming pool on a cool, breezy day has felt the heat loss that accompanies the evaporation of water from the skin. Our bodies use this same phenomenon to maintain a constant temperature: we perspire continuously, even when at rest, losing about mL of water daily by evaporation from the skin.

We also lose about mL of water as water vapor in the air we exhale, which also contributes to cooling. Refrigerators and air-conditioners operate on a similar principle: heat is absorbed from the object or area to be cooled and used to vaporize a low-boiling-point liquid, such as ammonia or the chlorofluorocarbons CFCs and the hydrofluorocarbons HCFCs. The vapor is then transported to a different location and compressed, thus releasing and dissipating the heat.

Thus heat pumps that use refrigerants are essentially air-conditioners running in reverse. Heat from the environment is used to vaporize the refrigerant, which is then condensed to a liquid in coils within a house to provide heat.

The energy changes that occur during phase changes can be quantified by using a heating or cooling curve. As the temperature of the ice increases, the water molecules in the ice crystal absorb more and more energy and vibrate more vigorously.

At the melting point, they have enough kinetic energy to overcome attractive forces and move with respect to one another. Once all the ice has been converted to liquid water, the temperature of the water again begins to increase. Now, however, the temperature increases more slowly than before because the specific heat capacity of water is greater than that of ice.

At this point, the temperature again begins to rise, but at a faster rate than seen in the other phases because the heat capacity of steam is less than that of ice or water. Thus the temperature of a system does not change during a phase change. Many cooks think that food will cook faster if the heat is turned up higher so that the water boils more rapidly.

At high temperature, gaseous water steam pushes a piston, which causes a wheel to turn. This is the essential mechanism by which steam-powered trains operate. In a reverse heat engine, a work input is converted to a heat output. In this case, the work generated by electricity condenses gaseous water steam and pushes it into a heat-exchange coil.

In the coil, the temperature of the water lowers as it liquefies, releasing heat to the environment. In , the Florida physician John Gorrie was granted the first U. Patent for a refrigeration machine, which uses a reverse heat engine Figure 2 as the first step in its operation.

Gorrie, convinced that the cure for malaria was cold because outbreaks were terminated in the winter, sought to develop a machine that could make ice and cool a patient's room in the hot Florida summer. In Dr. Gorrie's refrigerator, air was compressed using a pump, which caused the temperature of the air to increase exchanging work for heat. Running this compressed air through pipes in a cold-water bath released the heat into the water. The air was then allowed to expand again to atmospheric pressure, but because it had lost heat to the water, the temperature of the air was lower than before and could be used to cool the room.

Modern refrigerators operate by the same reverse-heat-engine principle of converting work to heat, but use substances other than air. The working substance in a modern refrigerators is called the coolant; the coolant changes from gas to liquid as it goes from higher to lower temperature. This change from gas to liquid is a phase transition, and the energy released upon this transition is mainly dependent on the intermolecular interactions of the substance.

Hence, to understand the refrigeration cycle used in modern refrigerators, it is necessary to first discuss phase transitions. Matter mainly exists in three different phases physical states : solid, liquid, and gas. A phase is a form of matter that is uniform in chemical composition and physical properties. As shown in Figure 3, a substance in the solid phase has a definite shape and volume; a substance in the liquid phase has no definite shape, but has a definite volume; a substance in the gas phase has no definite shape or volume, but has a shape and volume determined by the shape and size of the container.

This schematic diagram shows the differences in physical properties and particle arrangement between a substance in the solid, liquid, and gas phases.

In a solid, the particles are packed in a rigid configuration, giving the substance a definite shape and size. In a liquid, the particles are close together but may move with respect to one another, giving the substance a definite volume but a fluid shape.

In a gas, the particles may occupy the entire volume of the container, so that their shape and volume are both defined by the container. One of the major differences in the three phases illustrated in Figure 3 is the number of intermolecular interactions they contain. The particles in a solid interact with all of their nearest neighbors, the particles in a liquid interact with only some of the nearby particles, and the particles in a gas have almost no interaction with one another.

By breaking or forming intermolecular interactions, a substance can change from one phase to another. For example, gas molecules condense to form liquids because of the presence of attractive intermolecular forces. The stronger the attractive forces, the greater the stability of the liquid which leads to a higher boiling point temperature.

A change in the physical state of matter is called a phase transition. The names of the phase transitions between solid, liquid, and gas are shown in Figure 4.