chemistry Flashcards
what is the definition of an element
in an element all the atoms are the same
definition of a compound
Compounds contain two or more different elements chemically combined in fixed proportions
definition of a fixed proportion
a chemical compound always contains exactly the same proportion of elements by mass
definition of a mixture
In a mixture we have different elements or compounds but they’re not chemically combined
examples of physical separation techniques and why this would be used
This would be used if we wanted to separate mixtures. Examples include filtration, distillation, crystallization or chromatography
definition of a molecule
A molecule has any elements chemically combined even if they’re the same elements (e.g chlorine and oxygen)
In a specific compound what happens to the number of atoms in each element
In a specific compound the number of atoms of each element is fixed (we cannot change these numbers otherwise we have created a different compound)
give an example where changing the number of atoms affects the compound
CaSO4 (this is calcium sulfate)
CaSO3 (this is calcium sulfite)
definition of an insoluble solid, examples when it is used
Insoluble means that the solid will not dissolve in the liquid
one example is filtration
definition of a soluble solid, examples when it is used
soluble means that the solid will dissolve in the liquid
one example is crystallization
why do we have to be careful when speeding up crystallization by heating
It is not always a good idea because some chemicals can break down if they are heated
why can filtration not be used to separate magnesium chloride from water
This is because it is soluble and this means that it can be dissolved in water
define an exothermic reaction
it is where the products have less energy and are giving out heat
define an endothermic reaction
it is where the products have more energy and taking in surroundings making things cooler
