Topicm23a46db2ba6ce1e0_1528449000663_0Topic

Melting and solidification

Levelm23a46db2ba6ce1e0_1528449084556_0Level

Second

Core curriculumm23a46db2ba6ce1e0_1528449076687_0Core curriculum

I. Using physical terms and quantities to describe phenomena and to identify their examples in everyday life.

Timingm23a46db2ba6ce1e0_1528449068082_0Timing

45 minutes

General learning objectivesm23a46db2ba6ce1e0_1528449523725_0General learning objectives

Recognising basic physical processes.

Key competencesm23a46db2ba6ce1e0_1528449552113_0Key competences

1. Defines the conditions for the occurrence of phase transformations.

2. Determining differences between individual phase changes.

Operational (detailed) goalsm23a46db2ba6ce1e0_1528450430307_0Operational (detailed) goals

The student:

- recognizes basic physical processes,

- determines changes in the molecular structure of bodies during a physical process.

Methodsm23a46db2ba6ce1e0_1528449534267_0Methods

1. Learning through observation.

Forms of workm23a46db2ba6ce1e0_1528449514617_0Forms of work

1. Individual work.

2. Work with the whole class.

Lesson stages

Introductionm23a46db2ba6ce1e0_1528450127855_0Introduction

Task

Look at the illustration.

[Illustration 1]

Task

Answer the questions:

1. In how many states of mater does water exist on the Earth?
2. When does the water transform from one state of matter to another?
3. Name the physical processes presented in the picture which you know.m23a46db2ba6ce1e0_1527752263647_01. In how many states of mater does water exist on the Earth?
2. When does the water transform from one state of matter to another?
3. Name the physical processes presented in the picture which you know.

Answers:

1. Water on Earth occurs in a liquid state, solid (as ice) and gas (as steam).
2. At temperatures below 0°C, the water turns into ice and the water vapor in the clouds turns into snow. Above 0°C the water evaporates and condenses into small drops forming clouds. It can rain from clouds.
3. EvaporationevaporationEvaporation, liquefaction, meltingmeltingmelting, sublimationsublimationsublimation, resublimation.

Procedurem23a46db2ba6ce1e0_1528446435040_0Procedure

Task

Watch the slideshow „Melting of Wood's alloy”.
Note: Wood alloy - a low‑melting metal alloy (melts already at 66.5°C), silver‑gray, fine‑grained, consisting of bismuth, cadmium, lead and tin. It was received by an American dentist Barnabas Wood and was used in dentistry. This alloy is usually used: in jewellery for soldering.m23a46db2ba6ce1e0_1527752256679_0Watch the slideshow „Melting of Wood's alloy”.
Note: Wood alloy - a low‑melting metal alloy (melts already at 66.5°C), silver‑gray, fine‑grained, consisting of bismuth, cadmium, lead and tin. It was received by an American dentist Barnabas Wood and was used in dentistry. This alloy is usually used: in jewellery for soldering.

[Slideshow]

Task

Answer the following questions

1. What should be done to melt the solid?

2. Does the solid melt at any temperature?

3. How do solid particles behave while heating?

Answers

1. The solid body constantly requires to melt the energy delivery.

2. The solid melts at a strictly defined temperature.

3. Particles in the solid body vibrate only around the equilibrium positions, while in the liquid they move relatively. Thus, during meltingmeltingmelting, the body molecules gain greater freedom of movement.

MeltingmeltingMelting

MeltingmeltingMelting - phase transitionphase transitionphase transition in which transformation of a solid substance into a liquid state is observed.

The energy supplied to the solid causes overcoming binding forces between solid particles.

SolidificationsolidificationSolidification

SolidificationsolidificationSolidification - the liquid transformation into a solid state. The energy released by the liquid reduces the velocity of the particles, and the attraction forces connect them to a solid body. The start of solidificationsolidificationsolidification process depends on the presence of nucleation seeds in the liquid on which the crystal formation process begins.

EvaporationevaporationEvaporation

Evaporation - transformation of the liquid into a gas state. The energy supplied to the liquid overcomes the attractive forces between the molecules. The speed of the evaporationevaporationevaporation process depends on the temperature and the vapor pressure above the liquid.

CondensationcondensationCondensation

CondensationcondensationCondensation (Liquefying) - transformation of gas into a liquid state. The cooled gas releases energy, the velocity of particles decreases, the attraction forces make the particles to be closer. CondensationcondensationCondensation is associated with a reduction in the distance between the molecules of the substance. The drop in temperature causes the decrease in molecules motion speed. The forces of interaction between them increase until a new state of equilibrium is achieved.

SublimationsublimationSublimation

SublimationsublimationSublimation - the direct transfer of substances from solid to gas state without passing the liquid state.

Dry ice (solidified carbon dioxide) is an example of a sublimating body in normal conditions.

A block of frozen carbon dioxide, exposed in a room to a typical atmospheric pressure and the temperature about 20°C, will sublimate and will not melt.

Resublimation

Resublimation - direct transfer of a substance from a gas state to a solid one, omitting a liquid state. Resublimation is a process opposite to sublimationsublimationsublimation. Frost is created as a result of resublimation of water (steam). Resublimation, in combination with sublimationsublimationsublimation or evaporationevaporationevaporation, is used to purify or separate the substance and to obtain it in the form of fine crystals (this is, among others, iodine purification method).

Task

Complete the phase transformation scheme with the names of phase transitions next to the arrows (use the following names of phase transformations: meltingmeltingmelting, solidificationsolidificationsolidification, sublimationsublimationsublimation, desublimation, evaporationevaporationevaporation, condensationcondensationcondensation)

[Illustration 2]

Answer

[Illustration 3]

Lesson summarym23a46db2ba6ce1e0_1528450119332_0Lesson summary

- MeltingmeltingMelting is a change in the state of the body from solid into liquid. It occurs at a constant temperature, called the melting temperature.

- SolidificationsolidificationSolidification is a change in the state of the body from liquid to solid. This process can occur in the opposite direction (meltingmeltingmelting).

- Some bodies change from the solid to the liquid state without the established transition temperature. Within a certain temperature range, the body gradually softens and becomes liquid. This process is called softening.

- EvaporationevaporationEvaporation is the change in the state of the body in which the body transforms from liquid to gas. It occurs on the surface of the liquid.

- CondensationcondensationCondensation is a phenomenon of transforming steam or gas into the liquid state.

- SublimationsublimationSublimation is a phenomenon of a direct transition from the solid state to the gas state, omitting the liquid state.

- Resublimation is the phenomenon of direct transition from the gas to the solid state, omitting the liquid state.

Selected words and expressions used in the lesson plan

boilingboilingboiling

condensationcondensationcondensation

evaporationevaporationevaporation

freezingfreezingfreezing

meltingmeltingmelting

phase transitionphase transitionphase transition

solidificationsolidificationsolidification

sublimationsublimationsublimation