Thermodynamics Multiple Choice Quiz | Energy and Thermodynamics

Quiz Answer Key and Fun Facts

1. The word "thermodynamics" can be broken into 2 parts, namely "thermo" which means heat and "dynamics" which suggests in constant equilibrium or not static. Apart from the heat change that chemists are interested in, what other element or factor that they also study?

Answer: Work done

In the field of thermodynamics, chemists study the heat released or absorbed by a system. They also study the work done by the system. One very interesting application of thermodynamics is the manufacturing of artificial diamond. This can be done under the extreme condition of very high temperature and pressure.

However, the reaction rate is usually very slow and therefore, catalyst is used to speed up the process. Work is the dot product of vector force and vector length. Therefore, it is a scalar quantity.

2. A system is separated from its surroundings or universe by a boundary. In thermodynamics, there are 3 types of systems. An isolated system does not allow any heat and matter transfer between the system and its surroundings. On the other hand, for an open system, it allows both heat and matter transfer. What is the name given to the system that allows heat transfer but prevents matter transfer?

Answer: A closed system

Let's us look at an example. Let's say our system is a beaker with hot water in it and its surroundings are the air surrounding the beaker. Therefore, the boundary is the wall of the beaker.

If the beaker is insulated with cotton and closed with a lid, we say the beaker is an isolated system, since neither heat transfer nor matter transfer occurs.

If the beaker is closed with a lid but not insulated, it is a closed system because it allows heat transfer but not matter transfer.

Lastly, if the beaker is neither closed with a lid nor insulated, it is an open system, since the water molecules can escape or evaporate into the air (its surroundings, hence matter transfer) and also the heat is lost to the surroundings as time goes by (hence heat transfer).

3. Pressure, volume, internal energy, entropy and Gibb's free energy are all state functions because their values are dependent only on the initial and final state of the system, regardless of the route taken. On the contrary, non state functions are so-called because their values depend on the route taken. What are the two examples of non-state functions?

Answer: Work and heat

Both enthalpy and temperature are state functions. In thermodynamics, work is denoted by "w", while heat is denoted by "q".

4. There are two types of thermodynamics variables, namely intensive and extensive. Intensive variables are those that are independent of the amount of substance present in a system. For example, pressure and temperature. Meanwhile, extensive variables are those that are dependent on the amount of substance in the system. For instance, volume and mass. Is density an intensive variable or an extensive variable?

Answer: Intensive

Density = mass / volume. While both mass and volume are extensive variables, their ratio, namely the density is an intensive variable. The value of density remains constant no matter what amount of substance you consider. Hence, the density of a substance is independent of the size of the system. Therefore, we conclude that density is an intensive variable.

5. In thermodynamics, an isobaric process refers to a process that is carried out under constant pressure. Moreover, the terms isochoric and isothermal refer to constant volume and constant temperature respectively. What is the terminology used to describe a process that is carried out without any transfer of heat?

Answer: Adiabatic

For an adiabatic process, there is no transfer of heat. Adiabatic process can be further classified into reversible and irreversible.

6. When heat is absorbed by a system from its surroundings, the value of heat, q, is a positive value.

Answer: True

If heat is absorbed by a system from its surroundings, it refers to an endothermic process. Since heat is absorbed by the system, the value of q would be a positive value.

On the other hand, if heat is lost to the surroundings, the value of q would be a negative value. In this case, it is an exothermic process.

7. The total energy of a system, E consists of 3 types of energy. Which of the following is NOT one of them?

Answer: Resting energy, R

There is no such thing as resting energy; I just made that one up. The molecular rotational, translational, vibrational and electronic energies constitute the internal energy, U of a system.

8. Consider 3 systems, X, Y and Z. Given that X and Z are in thermal equilibrium. Y and Z also in thermal equilibrium. Then, X and Y will also be in thermal equilibrium. This is known as the zeroth law of thermodynamics.

Answer: True

There are all together 4 basic laws of thermodynamics. The zeroth law interrelates the thermal equilibrium between 3 systems. The first law is concerned with the law of conservation of energy. The second law deals with the direction of reaction and determines whether a reaction or process can occur by itself.

The third law is very useful to calculate the equilibrium constants for a specific reaction by using calorimetric measurements.

9. The First Law of Thermodynamics can be expressed mathematically by the equation delta U = q + w, where delta means change, U is internal energy, q is heat and w is work. What is the alternative name for this law?

Answer: The law of conservation of energy

We use delta U since we are comparing the values of the internal energy before and after a reaction or process. The law of conservation of energy states that energy can neither be created nor destroyed, but it can transform from one form into another.

10. Thermodynamics is a wide branch of discipline. Which branch of thermodynamics studies the changes of enthalpy of a reaction?

Answer: Thermochemistry

The change of enthalpy, delta H is a very useful quantity. It gives rise to the study of thermochemistry. The enthalpy change of a reaction can be determined by 2 methods, namely the direct calorimetry (an experiment is conducted in a calorimeter and the heat change is measured) or by using the Hess's Law (treating each chemical equation as mathematical equation, then by doing some algebraic manipulations, we arrive at the chemical reaction or equation that we desire).

Source: Author Matthew_07

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Thermodynamics Trivia Quiz

Thermodynamics is a branch of physical chemistry that studies the heat transfer between a system and its surroundings. Enjoy!

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