What mainly determines whether a substance is a solid, liquid, or gas at a given temperature?

The weight of the substance — heavier substances are always solid The balance between the kinetic energy of the particles and the strength of the forces of attraction between them The number of atoms — substances with fewer atoms are gases The colour of the substance — darker substances are denser and therefore solid

What is plasma — the fourth state of matter?

A very cold gas that has been compressed into a liquid-like state A high-energy state in which electrons have been stripped from atoms, creating a mixture of free electrons and positively charged ions The transparent state of matter found in window glass A mixture of liquid and gas that occurs just at the boiling point

You heat a block of ice. The temperature rises until 0 °C — then stays at 0 °C for a while even as you keep adding heat. What is happening?

The thermometer is broken — temperature always rises when heat is added The ice is absorbing heat from the thermometer, not from the flame The energy is breaking the bonds that hold water molecules in the solid structure (latent heat of fusion) rather than increasing the particles' kinetic energy Energy is temporarily stored in the water molecules and released later

What is condensation?

The change from liquid to solid, such as water freezing into ice The change from gas (vapour) to liquid, which happens when a gas loses enough energy for the forces of attraction to pull particles back together The process by which a solid absorbs moisture from the air The process of gases combining to form new molecules

Steam at 100 °C causes worse burns than liquid water at 100 °C. Why?

Steam is hotter than boiling water — it must be above 100 °C by definition Steam moves faster than liquid water and transfers heat by convection as well as conduction When steam condenses on your skin it releases extra latent heat — the energy that was used to boil the water — in addition to the heat from the temperature difference Steam contains dissolved gases that react chemically with skin

What does the First Law of Thermodynamics state?

Heat always flows from cold objects to hot ones Solids always have less energy than gases at the same temperature The total energy of a closed system is constant — energy cannot be created or destroyed, only transformed from one form to another Every action has an equal and opposite reaction

When sweat evaporates from your skin on a hot day, you feel cooler. Why?

The sweat absorbs heat from the sun, preventing it from reaching your skin Cold air rushes in to replace the evaporating water The molecules with the highest kinetic energy escape as vapour, carrying their energy away; the average energy of the remaining liquid drops, lowering its temperature The evaporation process creates cold, which is absorbed by your body

Which of the following would violate the Second Law of Thermodynamics?

A hot pan cooling down on a kitchen counter Ice melting in a warm room A cup of coffee left on a table spontaneously getting hotter while the surrounding room gets cooler Steam condensing on a cold window

Dry ice is solid carbon dioxide. At room temperature it turns directly from solid to gas — skipping the liquid stage entirely. What is this process called?

Condensation Evaporation Sublimation Deposition

A puddle of water slowly disappears on a cool day — well below the boiling point of water. How is this possible if boiling is required to turn liquid water to vapour?

Puddles boil silently due to pressure from the ground pushing water upward Evaporation can happen at any temperature because, at any temperature, a fraction of molecules have enough kinetic energy to escape the liquid surface Cool days have low humidity, which pulls water molecules out of puddles Water gradually converts to ice first, then ice sublimates into vapour