Video Transcript
Which of the following statements
best describes what calorimetry is? (A) The amount of energy produced
by the combustion of an item of food. (B) The amount of heat needed to
raise the temperature of one gram of a substance by one degree Celsius. (C) The measurement of the amount
of heat energy transferred in or out of a system during a chemical or a physical
change. (D) The amount of energy needed to
break one mole of bonds. Or (E) the measurement of the
change in the number of degrees of freedom that a system has.
A common way of measuring energy
changes in chemistry is to use a method known as calorimetry. Calorimetry is the study of heat
transfer during physical and chemical changes and relies upon the use of a piece of
equipment known as a calorimeter. A calorimeter is a device that
measures the amount of energy that is transmitted as heat as a result of physical or
chemical changes. It’s possible to think of it as a
self-contained or isolated system.
A common experimental setup for
calorimetry involves using an insulated reaction container, a stirrer, and a
thermometer. A polystyrene cup, supported in a
beaker with a close-fitting lid, is often used as an insulated container for the
reaction. In this setup, a reaction occurs in
the reaction mixture. The dissolved substances of
interest within the cup are often called the system, in which case the rest of the
reaction mixture is called the surroundings.
When most chemical reactions occur,
energy is released or absorbed. The law of conservation of energy
says that energy cannot be created or destroyed; it is only transferred. And during a reaction, the amount
of energy in two areas, the system and the surroundings, changes. The energy is always transferred
between the system and the surroundings. But what we define as the system or
surroundings can vary.
We assume that there is no heat
exchange between the calorimeter and the room. This is the key reason for the
insulating polystyrene used and the surrounding cotton wool. If a reaction occurring in the
system is exothermic, it releases energy to the surroundings, causing the
temperature to rise. This increase can be measured using
a thermometer.
And so, we can see that calorimetry
is a method for measuring energy change, as opposed to an actual quantity of
energy. So answer choices (A), (B), and (D)
must all be incorrect. The degrees of freedom, in answer
choice (E), is an advanced enthalpy concept that leaves us with answer choice
(C). Thus, the statement that best
describes what calorimetry is is (C), the measurement of the amount of heat energy
transferred in or out of a system during a chemical or a physical change.
