Sorry this will probably be pretty long.
So think of the "control" as being something you yourself add to increase or decrease the effects in an experiment.
I'll give you an example so it is not as confusing.
Say you have decided to make an experiment on plants. Which plant can grow the fastest on which type of liquid? What is being added to this experiment? The liquid! Or all of the liquids you used. Like if you used Coke, Lime Gatorade, Orange Gatorade, and Water. Each drink will EFFECT each plant differently.
Hope I was of any hope?
Answer:

Explanation:
Hello,
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:

Best regards.
Answer: True
The formula of weight is w = mg, where m is the mass and g is the acceleration of gravity. If you want to calculate an object's weight, you need to know the two components: mass and gravity.
You only need to know the mass of the object because the acceleration of gravity is ALWAYS (assuming the object is on Earth) 9.8 m/s^2.
Answer:
Both molarity and formality express concentration as moles of solute per liter of solution. Formality is a substance's total concentration in solution without regard to its specific chemical form. ... The formality of a solution is defined as the number of formula mass of any solute dissolved in 1 litre of solution.