Scientists should control most possible variables in experiments to get the most valid and correct data. If many variables are included in experiments it is more difficult to interpret what is causing a different outcome.
Answer:

Explanation:
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In this case, the molar enthalpy of reaction is obtained by dividing the involved energy by the reacting moles:

Thus, it is important to notice that the compound "uses" the energy, it means that it absorbs the energy, for that reason the sign is positive. Moreover, computing the result in kJ/mol we finally obtain:

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Chemical change creates a new substance
True. The building blocks of life are atoms
Answer:
Oxygen is a simple molecular structure, where individual oxygen atoms are bonded to each other by strong covalent bonds. Hence, a low amount of energy is required to overcome these weak forces and oxygen has a low boiling point. Therefore, at room temperature, oxygen is a gas. Oxygen difluoride is a colorless gas, condensable to a pale yellow liquid, with a slightly irritating odor. It is the most stable of the compounds of fluorine and oxygen, which include O,F,, O,F, and 0,F2 but nevertheless it is a strong oxidizing and fluorinating agent. Oxygen Difluoride is a colorless gas or a yellowish-brown liquid with a foul odor. Just to finally link Joseph's answer to the question, oxygen difluoride will thus change from liquid to solid state when chilled from -220°c to -230°c. The boiling point of oxygen is -182.96 degrees Celsius (under 1 standard atmosphere). This means at temperatures below that point, oxygen is a solid or a liquid, and at temperatures above that point, oxygen is a gas. So at -183 degrees Celsius, oxygen is a liquid.
Explanation: