A chemist (from Greek chēm (ía) alchemy; replacing chemist from Medieval Latin alchimista[1]) is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms. Chemists carefully measure substance proportions, reaction rates, and other chemical properties. The word 'chemist' is also used to address Pharmacists in Commonwealth English.
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The reaction that the graph represents is
A. Exothermic because Hrxn=-167 kJTo calculate Hrxn we apply the following equation:

Looking at the graph, and at the result of the calculations, we can see that the enthalpy of the products is
lower than the enthalpy of the reagents, because the sign is negative. That means that the reaction
releases energy in the form of heat and that the reaction is
exothermic.
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Sorting the chemical elements in order from least reactive to most reactive, we have:
1. Fluorine (F).
2. Arsenic (As).
3. Antimony (Sb).
4. Silicon (S).
<u>Given the following chemical elements:</u>
Reactivity can be defined as a chemical property which determines how readily a chemical element <u>bonds</u> with other chemical elements, in order to form a new chemical compound.
Generally, the ability of a chemical element to bond with other chemical elements is largely (highly) dependent on the number of valence electrons it has in the outermost shell of its atomic nucleus.
As a general rule, chemical elements that are having <u>fewer</u> number of valence electrons are the most reactive while those having <u>higher</u> valence electrons are least reactive.
Also, chemical reactivity <u>decreases</u> down a group on the periodic table.
Based on the periodic table, the valency for the given chemical elements are:
- <u>Antimony (Sb):</u> 5 valence electrons.
- <u>Silicon (S):</u> 4 valence electrons.
- <u>Fluorine (F):</u> 7 valence electrons.
- <u>Arsenic (As):</u> 5 valence electrons.
In conclusion, sorting the chemical elements in order from least reactive to most reactive, we have:
1. Fluorine (F).
2. Arsenic (As).
3. Antimony (Sb).
4. Silicon (S).
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