Chemistry · Structure 1: Models of the particulate nature of matter. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
All matter is made of particles. An element contains only one kind of atom. A compound contains atoms of different elements chemically bonded in a fixed ratio. A mixture contains substances that are not chemically bonded, so it can be separated by physical methods. A homogeneous mixture is the same throughout (a solution, air); a heterogeneous mixture is not (sand in water).
In a solid the particles are close together and vibrate about fixed positions. In a liquid they are close but can move past each other. In a gas they are far apart and move quickly at random.
During a change of state the energy changes the spacing of the particles, so the temperature stays constant.
Comparing kinetic energies with Celsius temperatures. Heating from 20 °C to 40 °C does not double the average kinetic energy; convert to kelvin first (293 K to 313 K).
Answer: 373 °C (646 K)
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