Thermodynamics - The Heat Is On Quiz

Answer: Energy is released to the surrounding areas whose temperature increases

An exothermic reaction can be either physical or chemical. It involves the breaking of a bond to create a new bond and if the energy that is needed to break the old bond is more than the energy in the new bond then that surplus energy is released to the surrounding areas as heat.

A good example is a match being struck. The chemicals in the matchhead and the striking surface represent the old bonds. Striking it provides the energy that re-arranges the atoms of the chemicals to create a new bond, thereby forming a new molecule. The energy contained in the new bond is less than the energy obtained from striking the match and, as a result, heat is given off.

This is in accordance with the First Law of Thermodynamics which states that "energy cannot be created or destroyed, merely changed from one form to another". In other words, the extra energy cannot simply disappear or be destroyed. In this example of a struck match, the excess energy is converted into heat.

This question was created by Phoenix Rising team member pollucci19.

Answer: Surface

The energy given off in an exothermic reaction is usually transformed into heat, such as a candle's flame or a struck match. However, other transformations can also occur. Examples include light from sparks and flashes, electricity from batteries, and sound from explosive events.

This question was created by Phoenix Rising team member purelyqing.

Answer: The heat content during a chemical reaction

Enthalpy can also be defined as the total energy of a thermodynamic system; however, we figured that "heat content" would come across as more of a layman's term. This measure is usually signified by the letter "H".

The measure of the disorder in a system is entropy. A protein that speeds up a reaction is an enzyme. An atom defined by its atomic number is an element.

This question was created by Phoenix Rising team member pollucci19.

Answer: Less energy in end product, negative change in enthalpy

In an exothermic reaction, the end product would have less energy than its starting reactants because the excess energy would have been released into its surroundings. Subtracting the energy in the starting reactants (larger value) from the end products (smaller value) would give a negative value.

This can be better illustrated as a mathematical equation:

End energy - Starting energy = Change in enthalpy

In an exothermic reaction,

End energy = lower
Starting energy = higher

Therefore,

Lower value - Higher value = Negative value

This question was created by Phoenix Rising team member purelyqing.

Answer: Endothermic reaction

Generally the energy that is absorbed in an endothermic reaction is heat, though this is not always the case. Other forms, such as electrical energy, can be taken in. A couple of common examples of endothermic reactions are photosynthesis and an ice cube melting.

The French chemist Marcellin Berthelot was reported to have coined the term "endothermic" and its roots lie in the Greek terms "endon", meaning within, and "therm", meaning hot.

This question was created by Phoenix Rising team member pollucci19.

Answer: One-way direction

Under the Second Law, a spontaneous process has a tendency to achieve a more disordered state. In other words, the natural course of events brings an isolated system to a state of higher entropy, entropy being a measure of the system's disorder.

As an example, when liquid water is added to alcohol the molecules of both liquids spontaneously mix, bringing the system to a higher state of disorder (higher entropy). The water molecules will not spontaneously separate from the alcohol molecules to create one discrete section of water and another discrete section of alcohol. Therefore the mixing of alcohol and water occurs in a one-way direction only.

This gives rise to the "arrow of time" concept, which is essentially "before and after". If provided with two states of a system, one less disordered and one more disordered, it can be assumed that the more disordered state occurred later in time.

This question was created by Phoenix Rising team member purelyqing.

Answer: Water forming into ice

The Third Law states in simplistic terms that at absolute zero (temperature - 0 degrees Kelvin) the entropy is zero. As we can approach a state of near zero temperature we can approach a near zero degree of entropy but we can never quite reach either and we certainly never reach negative entropy. We can however have decreasing entropy which occurs when temperatures decrease. From the examples given, three phase changes show the effects of increasing temperature (water changing to water vapour, ice changing to water and CO2 changing from a solid to a gas [without going through a liquid phase]) but only one reaction shows a decreasing temperature (water, by definition, has a temperature of greater than 0 degrees Celsius whereas ice must be less than or equal to 0 degrees Celsius by definition).

This question was created by Phoenix Rising team member 1nn1.

Answer: Zeroth

The Zeroth Law of Thermodynamics defines thermal equilibrium. If System A is in thermal equilibrium with System B, and System B is in thermal equilibrium with System C, then System A and System C are also in thermal equilibrium with each other.

A classic example of the Zeroth Law is the thermometer. Because two systems that are in physical contact will be in thermal equilibrium with one another, a calibrated instrument (i.e. the thermometer) can be used to determine the property of thermal equilibrium (i.e. the temperature) of the system that it is in contact with.

The Zeroth Law was established after the first three laws of thermodynamics were postulated. However, because of its importance as the very definition of thermal equilibrium (a property we know as temperature), the Zeroth Law should rightfully head the list. Therefore it was named the Zeroth (0th) Law to precede the existing three laws.

This question was created by Phoenix Rising team member purelyqing.

Answer: adiabatic

The walls or boundaries of a system (whether actual or merely notional) constitute a fundamental physical entity in thermodynamics. Systems may be defined as:

Open - allow transfers of matter and usually energy
Closed - allow transfers of energy (as heat or work) but not matter
Adiabatic (or adiabatically isolated) - allow transfers of energy as work but not matter or energy as heat
Adynamic (or purely diathermically isolated) - allow transfers of energy as heat, but not matter or energy as work
Isolated - do not permit transfers of matter or energy

This question was created by Phoenix Rising team member JCSon.

Answer: The rate of cooling in black coffee is greater than white coffee but you can drink white coffee sooner

Where there is a larger difference between two temperatures, the rate of cooling is greater.

There are three temperatures in this scenario: the initial temperature of the black coffee near boiling point (TB), the temperature of the white coffee immediately after milk is added to the near boiling coffee (TB-n), and the temperature at which cooling coffee can be first drunk (TD).

As TB is greater than (TB-n), the rate of cooling between TB and TD will be greater than the rate of cooling between (TB-n) and TD. However the added milk to black coffee immediately drops the temperature of the white coffee. Therefore while the rate of cooling to drinkable temperature in white coffee is less, the difference between the initial (white coffee) temperature and the drinkable temperature is less than the difference between the initial (black coffee) temperature and the drinkable temperature, hence the drinkable temperature is reached earlier in white coffee than black coffee.

(This is actually a true story. I asked the Biology teacher if I could explain on the black board. I used calculus and derivatives to explain why she was wrong. I then had to repeat the exercise in front of all the science faculty. I was mortified (but vindicated)).

This question was created by Phoenix Rising team member 1nn1.