الأسبوع 15 · مراجعة الفصل الدراسي الأول (الوحدات ١–٤) ومهام مراجعة من إعداد Darslab · 3 دروس
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Review: states of matter and heat
Science Prep 2 Term 1, Units 1–4: Review
GoalReview states of matter, changes of state, heat and temperature, and the three ways heat moves, with new mixed tasks.
New words
particle model · matter is made of moving particles with attractions and spaces between themheat · energy that moves because of a temperature differencespecific heat · the heat to warm 1 kg of a substance by 1 °Cconduction, convection, radiation · the three ways heat is transferred
Explanation
Here is what to remember from Unit 1. Matter has solid, liquid, gas and plasma states; the particle model explains them by the spacing, the attractions and the motion of particles. When energy is gained, the particles move faster and the temperature rises, except in the flat parts of a heating curve, where the energy weakens the attractions: melting and boiling. Melting, boiling and sublimation gain energy; freezing, condensation and deposition lose energy. Evaporation is a surface change at any temperature, faster when warmer, with a bigger surface, drier air or moving air. A system can be open, closed or isolated. Temperature measures the average kinetic energy of particles, internal energy is the total, and heat is the energy that flows from hot to cold. The same heat warms a small mass, a low-specific-heat material and ice more. Heat moves by conduction (particles bump in solids), convection (moving fluids) and radiation (waves that need no material). Use the invented curve for substance Z (melting point 40 °C, boiling point 120 °C).
Worked examples
Read the curve of substance Z. Part 1 (0–4): the solid warms to 40 °C. Part 2 (4–10): flat at 40 °C, melting. Part 3 (10–18): the liquid warms to 120 °C. Part 4 (18–24): flat at 120 °C, boiling. Part 5: the gas warms. At 80 °C the substance is a liquid, between 40 °C and 120 °C.
Name each change and say whether energy is gained or lost: solid iodine becoming vapour (sublimation, gained); frost forming on a cold window (deposition, lost); a wet road drying (evaporation, gained).
Mix 100 g of water at 70 °C with 100 g at 30 °C. Equal masses, so the final temperature is the average, (70 + 30) ÷ 2 = 50 °C, ignoring losses. Heat flowed from the hot water to the cold water until equilibrium.
Class activity
Unit 1 poster, with a grown-up. On one page draw (1) the three states as particle boxes, (2) a heating curve of your own invented substance with its melting and boiling points, and (3) three arrows labelled conduction, convection and radiation with one everyday example each. Write one sentence under each drawing. Do not heat anything: use only invented numbers and kitchen examples.
Practice
1
Substance Z has a melting point of 40 °C and a boiling point of 120 °C. What is its state at 25 °C, 80 °C and 150 °C?
Solid at 25 °C, liquid at 80 °C, gas at 150 °C.
2
Which box shows a gas?
C: the particles are far apart and move freely.
3
In the flat part of the curve at 40 °C, where does the supplied energy go?
It pulls the particles apart (potential energy rises) while the temperature stays constant.
4
A lidless pot, a closed jar and an ideal perfect flask: classify each as open, closed or isolated.
Open, closed, isolated.
5
Conduction, convection or radiation? (a) a spoon warming in tea, (b) warm air rising from a heater, (c) warmth from the Sun.
(a) conduction, (b) convection, (c) radiation.
6
Two cups hold water at 30 °C: one 100 g, one 300 g. Compare temperature and internal energy. Name three ways to make evaporation faster.
Same temperature; the 300 g cup has more internal energy. Faster evaporation: warmer, bigger surface, drier air or moving air.
