Changes In Energy On The Molecular Level Notes - Merryhill School

Changes in Energy on the Molecular Level

States of Matter Review When a material is in a solid state, the atoms are packed closely together. There is minimal space between them. Solid structures have a specific shape and volume. Molecules in a solid do not flow. Instead, they stay at the same position, resulting in the solid holding its shape. Unlike molecules in a solid state, molecules in liquid form flow. When a material is in a liquid state, the atoms are packed more loosely, creating a structure with a definite volume but no definite shape. This means that even though we can measure how much space is being taken up, the actual shape of the object changes. When a material is in a gas state, its atoms are spread out freely; gases have no definite shape or volume.

Discussion We interact with solids, liquids, and gases on a daily basis. Can you think of some examples of when we need these three states of matter for our survival? List one of each state and the rationale, or reason.

Effect on Atoms Thermal energy is the combination of the kinetic and potential energy of the particles which make up the substance. The flow of thermal energy between a substance and its surroundings is known as heat flow and can be measured with a thermometer in the lab. Thermal energy flow and state changes are dependent on the temperature and pressure of the system as well as the composition of the substance.

Effect on Atoms (continued) The addition (and removal) of thermal energy can cause materials to change characteristics. When heat is added, the molecules and atoms vibrate faster. As the vibrations speed up, the space between atoms increases. In the case of solids, this would cause melting to occur. The once solid item would now be a liquid.

Effect on Atoms (continued) If increased heat was added to a liquid, it is likely that the liquid’s atoms would similarly separate and push apart if the temperature was hot enough. This would result in yet another change in the state of matter. You have likely seen this with boiling a substance. With water, for example, a temperature of 100 degrees Celsius would create conditions for the liquid to become a gas. Do note, however, that this exact temperature is a property of water. This is not a universal temperature that fits all materials. It is unique to water!

Phase Changes Phase changes can be caused by changes in temperature, changes in pressure, or a combination of both. Temperature is a measurement of the average kinetic energy of the molecules in an object or system. It does not depend on the number of molecules in the system. Heat is a measure of the energy transferred from one object or system to another. Heat moves from a higher temperature to a lower temperature. When there is no difference in temperature, no heat flow occurs. Pressure is defined as force per unit area.

Phase Changes (continued) The average kinetic energy of the molecules in the solid increases as heat is added to a solid. This raises the temperature of the substance. Under normal atmospheric pressure, the solid will melt into a liquid. While the solid is melting, the temperature does not change. Energy goes into the phase change, breaking the attractive bonds, without an increase in molecular speed. This is a change in potential energy, not kinetic energy. With continued addition of heat, the liquid will turn into a gas. While the liquid is vaporizing, the temperature again does not change. The amount of energy that must be added to change the temperature of a substance depends on the substance and its phase. A phase diagram graphing temperature on the x axis and pressure on the y axis can show the phase transitions of a particular substance.

Discussion In the picture above, there are some changes happening to the liquid. What are they? List three changes that are occurring. Be sure to use science terminology that includes matter and thermal energy. For example, the liquid state of water is boiling. After discussing, write your response in your notes.

Discussion Describe how the different weather conditions of Picture A and Picture B would affect the concrete in the roads, and what the construction teams might need to consider when choosing materials for each road.

Answer Picture A - weather conditions are very cold, materials used in the road would need to be able to contract as the molecules move closer together and vibrate less. Picture B - weather conditions are very hot, materials used in the road would need to be able to expand as the molecules move farther apart and vibrate more.

True or False? In the chart below, use true or false to determine which statements are accurate and which are not. After writing down your reply on the black line, provide the evidence in favor of or against the statement. Use the last illustration column to provide a visual.

Thermal energy is the combination of the kinetic and potential energy of the particles which make up the substance. The flow of thermal energy between a substance and its surroundings is known as heat flow and can be measured with a thermometer in the lab. Thermal energy flow and state changes are dependent on the