1.Complete the following sentences, using the words or groups of words in the box below. You may use some words more than once.
|• as small as possible |• decrease |• molecules |• quantities | |• balance |• different |• nature |• rearranging | |• bonds |• equal |• never |• release of a gas | |• characteristic properties |• heat |• new elements |• rules | |• check |• increase |• nuclear |• signs | |• chemical |• law of conservation |• nucleus |• state | |• chemical equation |of mass |• physical |• stoichiometry | |• coefficient |• mass of products |• precipitate |• subscript symbols | |• colour |• mass of reactants |• products |• transformed | |• counting |• molar mass |• proportions |• whole numbers |
a)There are three types of changes in matter: ________________________ changes, chemical changes and ________________________ changes.
b)A physical change occurs when the form or the ________________________ of a substance is changed. For example, when liquid water is cooled, it becomes ice. Whether water is in liquid form or in the form of ice, the ________________________ that form water remain the same. The ________________________ of water do not change.
c)A ________________________ change alters the ________________________ of a substance. The very nature of the ________________________ is altered: they are no longer the same after the change. This transformation involves ________________________ the bonds between the atoms and forming new molecules.
d)A ________________________ transformation involves changes that occur in the ________________________ of the atom. The transformation causes the atoms to split and form ________________________. e) Chemical changes occur when the ________________________ between reactants (initial substances) are broken to form new ________________________ (final substances), whose characteristic properties are ________________________. During this process, the quantities of reactants ________________________, and the quantities of products ________________________.
f) We can recognize that a chemical change has taken place by certain ________________________: the ________________________, the emission or absorption of ________________________, the emission of light, a change in ________________________, and the formation of a ________________________.
g) A chemical change, or chemical reaction, can be represented by a ________________________, which shows how the change took place. It is useful to identify the ________________________ of the substances (solid, liquid, gas or aqueous solution) with ________________________ in parentheses to the right of the substance.
h) The scientist Antoine Laurent de Lavoisier made this famous statement that explains the________________________: "Nothing is lost; nothing is created; everthing is ________________________." This means that the ________________________ before the chemical reaction is equal to the ________________________ after the reaction.
i) To follow the law of conservation of mass, we must...