Terry heats two different masses of substance a to different temperatures, and measures the amounts of both carbon dioxide and water produced.
which statement is true about this experiment?
this experiment is uncontrolled because two different masses of substance a are used.
this experiment is well controlled because only the mass of substance a is varied.
this experiment is uncontrolled because two gaseous products are measured.
this experiment is well controlled because the masses of substance a and the products are varied.

This experiment is uncontrolled because two different masses of substance A are used.

Explanation:

A controlled experiment is a structured experiment aimed at testing a particular observation or observations. The setup of a controlled experiment helps to determine the reason why a particular observation occurs and what must have led to it.

In the experiment highlighted above, different masses of a substance were used, they were heated to different temperatures. The set up does not show any correlation between the masses of substances heated and the temperatures. It is even difficult to try to predict the hypothesis for this kind of experimental set up. All the variables in play can best be assumed to be independent of one another.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.