Matter is a substance made up of different types of particles that occupy physical space and have mass. Matter is the makeup of the universe. Solid, liquid, and gas are the three general states of matter on earth.
The molecules of water move differently depending on the state of matter. In the gas form they move freely, in the liquid form they have a more restricted range of movement, and in the solid form they are not changing positions but vibrating in place
Figure 2: Three states of water molecules.
Solid is hard; have a solid shape and volume. The liquid takes the shape of its container; it has a different volume but no particular shape. Gases, also known as vapors, take on the volume and shape of their container; it does not have a definite shape and volume. The arrangement of the molecules in a substance determines the different properties of solids, liquids and gases.
Read on for some thoughts on why this can be a boring subject for teachers and students, five suggestions to improve this outcome, and thoughts on why our virtual labs can be beneficial
There are three main reasons why heating curves and phase changes can be difficult for even the most diligent student.
Heating curves and phase changes occur at the molecular level, which cannot be seen or felt. Not being able to visualize the process and not see its relevance to the real world can discourage learning and make it difficult for students to stay motivated.
Phase change: The state of matter depends on the intermolecular forces (IMF) and kinetic energy (KE) of the particles - be they molecules, ions, or atoms. The chemical identity of the particles in a liquid determines the nature and strength of the intermolecular attractions.
The change in energy in the system determines the phase change. To move from one state of matter to another, we need to add enough energy to overcome the intermolecular forces holding the particles together.
Figure 3: Phase changes
The phase changes as it occurs naturally:
Melting: The energy required to break intermolecular forces and increase particle motion during a solid-liquid transition is called the heat of fusion or enthalpy of fusion (ΔHfus). In chemistry, melting is referred to as fusion.
Evaporation: The speed of particle movement continues to increase with increasing temperature. The motion of the particles becomes faster and farther away as the particles transition to the gaseous state. At this point, even less intermolecular forces hold the molecules together. The transition from liquid to gas is called evaporation. The energy involved in this phase change is called the heat of vaporization or enthalpy of vaporization (ΔHvap).
Sublimation: Some solids can omit the liquid phase and go straight to the gaseous state. The transition from solid to gas is called sublimation. The energy required for sublimation is called the heat of sublimation or the enthalpy of sublimation (ΔHSub). In general, the heat of sublimation is much greater than the heat of vaporization, with the heat of fusion being the smallest. This is because all intermolecular forces are broken in the gaseous state, while in liquids, they are intact, and in solids, they are completely intact. More energy is required to break all intermolecular forces between particles.
With those points in mind, here are five things you can incorporate into heating curves and phase change classes to make them more engaging, accessible, and fun for you and your students.
A phase diagram is a graph that shows the phase of a substance as a function of temperature and pressure. The diagram shows the phase transition temperatures (melting point, sublimation point, boiling point) at different pressures.
Figure 4: water phase diagram. The pressure and temperature axes are not drawn to the scale.
The important elements to be extracted from the water phase diagram are
Triple point: the point where all three phases coexist in equilibrium. At pressures below the triple point, water cannot be a liquid, no matter the temperature.
Melting Point: ice is melted at this point.
Boiling point: The temperature at which water evaporates.
Critical Pressure: The pressure required to liquefy a gas at its critical temperature.
Critical point: Critical temperature and critical pressure of a substance. Beyond the critical point, the physical properties of water fall somewhere between gaseous and liquid states. This condition is called supercritical fluid.
The heat curve is a graph of the temperature versus the amount of heat input. The heating curve shows the change in temperature that occurs as a substance absorbs an increasing amount of heat. We can also observe that the temperature remains constant as long as a change in state occurs. The temperature plateaus due to the fact that all the heat energy is used to break the intermolecular forces.
Latent heat (kJ/mol) is the change in total heat energy involved in the phase change. Three types of latent heat are involved as follows:
The latent heat of fusion or enthalpy of fusion (Δ_H_fus) is the amount of heat required to change one mole of a substance from solid to liquid.
The latent heat of evaporation (Δ_H_vap) is the amount of heat required to change one mole of a substance from a liquid to a gaseous state.
The latent heat of sublimation can be estimated as the sum of the enthalpy of fusion and the enthalpy of vaporization.
Distillation is a powerful method for separating the elements of a homogeneous mixture. The distillation technique utilizes differences in boiling points. The reaction mixture is heated to the boiling point of the most volatile liquid. The most volatile substances are evaporated first and vapor is formed within the distillation apparatus. The vapor is then condensed back into a liquid after passing through the condenser and finally collected in a collection flask.
The condenser is one of the major parts of the distillation apparatus. The upper part is connected to the distillation flask and thermometer via an adapter, the lower part is connected to the collecting flask. The most popular condenser has 2 hollow chambers. Cold water continues to flow in the outer chamber, which cools the glass condenser. Water enters the condenser at the bottom and exits at the top. When the hot steam enters the inner chamber of the condenser, it is cooled by the cold surface, condenses, and flows into the collection flask. This setting prevents the hottest steam from touching the coldest water, avoiding heat shock to glassware.
Figure 6: Process overview of ethanol distillation
A unique way to teach heating curves and phase changes is through a virtual laboratory simulation. At Labster, we’re dedicated to delivering fully interactive advanced laboratory simulations that utilize gamification elements like storytelling and scoring systems, inside an immersive and engaging 3D universe.
Check out the Labster heating curves and phase changes simulation that allows students to learn about heating curves and phase changes through active, inquiry-based learning. In the simulation, students will learn how to generate and interpret the heating curves of ethanol and water.
Learn more about the heating curves and phase changes simulation here or get in touch to find out how you can start using virtual labs with your students.
Virtual Labs are interactive science simulations that accelerate STEM learning through gamification. Educators assign labs to students through their internet browsers, where students can train lab skills, visualize abstract theory, and learn science through real-world scenarios.
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