S1.1 Introduction to the particulate nature of matterIB Chemistry HL: Flashcards
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Define an element.
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- Define an element.
- A substance that cannot be broken down into simpler substances by chemical means.
- Define a compound.
- A substance containing atoms of different elements chemically bonded together in a fixed ratio.
- Define a mixture.
- Two or more elements or compounds, not chemically bonded, in no fixed ratio, which can be separated by physical methods.
- How does the melting behaviour of a pure substance differ from that of a mixture?
- A pure substance melts sharply at one temperature; a mixture usually melts over a range of temperatures.
- Give an example of a homogeneous and a heterogeneous mixture.
- Homogeneous: salt solution, air or an alloy. Heterogeneous: sand in water or oil and water.
- What does temperature in kelvin measure?
- The average kinetic energy of the particles (average Ek is proportional to T in K).
- Convert 25 °C to kelvin.
- 25 + 273 = 298 K.
- Convert 0 K to °C.
- −273 °C (−273.15 °C).
- Why does temperature stay constant while a pure substance boils?
- The energy supplied is used to overcome the attractions between particles (increasing potential energy), so the average kinetic energy, and hence the temperature, does not change.
- Describe particles in a solid, a liquid and a gas.
- Solid: close, regular, vibrating about fixed positions. Liquid: close, irregular, sliding past one another. Gas: far apart, random, moving fast.
- What is sublimation?
- A change of state directly from solid to gas, e.g. CO₂(s) → CO₂(g).
- What do the state symbols (s), (l), (g) and (aq) mean?
- Solid, liquid, gas and aqueous (dissolved in water).
- Which is longer on a heating curve, the melting or the boiling plateau, and why?
- Boiling, because separating particles completely needs much more energy than loosening them from fixed positions.