8TH GRADE PRACTICE
Physics Problems: Change in state of aggregation, Grade 8
Melting, evaporation, moisture and boiling.
Here the conditions and analysis of the solution can be read without an account. In the simulator, you need to collect the same analyzes yourself: “Given,” formulas, order of steps and answer.
Problem statements
The answer options are there to check against, and the walkthrough opens under each problem.
Problem #13
Melting, crystallization and graphsEvaluate the statement: Melting turns a solid into a liquid, and crystallization is the reverse transition.
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For a pure crystalline substance, both processes at a given pressure occur at the same temperature.
Answer
Problem #14
Melting, crystallization and graphsEvaluate the statement: The concept “Melting point” means: The graph shows the change in temperature over time and allows you to see areas of heating and phase transitions.
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During the transition, the supplied energy destroys the ordered bonds, so the temperature temporarily remains constant.
Answer
Problem #15
Phase transitionsHow much heat is needed to melt 0.5 kg of ice at 0 °C? The specific heat of fusion is 334 kJ/kg.
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Answer
Problem #16
Evaporation, condensation and humidityEvaluate the statement: Steam is saturated when evaporation and condensation in a closed volume occur at equal rates.
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Unsaturated steam allows further preferential evaporation, and the density of saturated steam depends on temperature.
Answer
Problem #17
Evaporation, condensation and humidityEvaluate the statement: The concept of “Evaporation and condensation” means: The ratio of the actual content of water vapor to the saturated one at the same temperature, expressed as a percentage.
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Evaporation is accelerated by heat, wind, and increased surface area; The fastest molecules carry away energy and cool the liquid.
Answer
Problem #18
HumidityThe density of water vapor in the room is 8.5 g/m³, and the density of saturated vapor at the same temperature is 17 g/m³. Find the relative humidity.
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Answer
Problem #19
Boiling and vaporizationEvaluate the statement: Intense vaporization throughout the entire volume of liquid with the formation and growth of vapor bubbles.
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Boiling begins when the saturated vapor pressure is equal to the external pressure.
Answer
Problem #20
Boiling and vaporizationEvaluate the statement: the concept “Specific heat of vaporization” means: The boiling point decreases as the external pressure decreases and increases as it increases.
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When condensing the same mass of steam, the same amount of energy is released in modulus.
Answer
Problem #21
BoilingTo convert it into steam, take 0.2 kg of water at boiling point. The specific heat of vaporization is 2.3 MJ/kg. Find the required heat.
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Answer
The theory behind these problems
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Formulas by topic
Look up symbols and units of measurement in the reference.