Fahrenheit 111 Trivia Quiz

Answer: Alkali metals

The Periodic Table, first formulated by Dmitry Mendeleev when he listed elements in order of increasing atomic mass, shows relative trends down its columns (groups), rather than across its rows (periods). All elements in Group I are alkali metals, Group II contains alkaline earth metals, Group XVIII contains noble gases, etc.

Other alkali metals include cesium, sodium, potassium, and lithium. In general, alkali metals are extremely reactive, and easily form ionic compounds. In fact, sodium is so reactive that it must be stored in oil, because it can catch fire when introduced to water! Atomic clocks are frequently constructed using rubidium and cesium.

Answer: London dispersion forces

Intermolecular attractive forces have a large impact on a compound's overall properties. When two molecules attract each other, for instance, in liquid, they form a sort of "film" that increases surface tension. With large intermolecular attractive forces, boiling point increases as well.

The most common type of intermolecular attractive forces is called the London dispersion force, and it's caused by the random movement of electrons around a molecule. Electron density is constantly changing, creating regions of positive and negative charge that last for brief periods of time, called instantaneous dipoles. Nearly all molecules exhibit dispersion forces, which occur when negative instantaneous dipoles of one compound attract the positive dipoles of another. The larger the molecule, the stronger the dipoles, because the electron cloud is larger in volume and more easily polarized. Thus, n-pentane, which has a relatively large surface area with a five-carbon backbone, will have strong dispersion forces.

A permanent dipole, however, will be stronger than instantaneous dipoles, and these arise in molecules with polar bonds. Electronegativity is the ability of an atom in a bond to attract electrons to itself. Atoms with high electronegativity (halogens like fluorine, as well as oxygen and nitrogen) are often slightly negative in compounds, because they attract electrons best. Since the molecule is overall neutral, the other atoms gain a slight positive charge, because they mostly lost their electrons. The molecule has positive and negative poles, which respectively attract the negative and positive poles of other molecules, forming stronger intermolecular attractive forces. These "dipole-dipole" interactions are exemplified by a particularly strong form of the phenomenon, called hydrogen bonding, which occurs when hydrogen (low electronegativity) is bonded to nitrogen, oxygen, or fluorine in a compound. Hydrogen bonding accounts for water's strong intermolecular attractive forces that lend it a very value for high boiling point, specific heat capacity, solvation ability, and surface tension.

Answer: Molecular velocity will double

A gas' average kinetic energy, or energy of motion, is given by the equation K = 3/2*Kb*T, where Kb stands for Boltzmann's constant, approximately 1.38 *10^-23, and T is absolute temperature (in Kelvins). For a given particle, kinetic energy is also equal to the product of 1/2 times the mass of the particle, times its speed squared (1/2mv^2). Rearranging the equation yields the relationship that average velocity equals the square root of three, times the ideal gas constant R, times temperature, all divided by the gas' molar mass. This "average" speed is often referred to as a gas' "root mean square" or RMS velocity.

Because of that mathematical relationship, temperature is proportional to the square of the gas' speed, so if the speed doubles, temperature is multiplied by 4. Velocity is also inversely proportional to the square root of the gas' molar mass, which can be used to derive Graham's Law of Effusion. That law states that gases of heavier elements in general travel more slowly than lighter gases. If you open a canister of helium and a canister of radon from one side of the room, the helium will move much more quickly than the radon, because helium has a significantly lower molar mass.

Answer: Its pressure would increase

The gas would either expand, or its pressure would increase, according to the ideal gas law. As its particles move faster at higher temperatures (and kinetic energy), they will collide more frequently with the walls of the containers, and exert an outward force over the container's surface. We call that pressure.

The ideal gas law combines three separate gas laws (Charles' Law, Boyle's Law, and Guy-Lussac's Law), as well as Avogadro's discovery that equal volumes of gas at standard temperature and pressure contain equal moles of gas, into a simple equation: PV = nRT. P is pressure, usually measured in kilopascals or atmospheres; V is volume; n is the number of moles of gas; R is the ideal gas constant, which does not change and equals 0.0821 L atm mol^-1 K^-1; and T is absolute temperature, in Kelvins. The ideal gas law isn't a universal statement, as it only applies when a gas behaves ideally: that is to say, at high temperatures and low pressures, when individual particles have negligible volume, and attractive forces between molecules are ineffective. Corrections to the ideal gas law, perhaps most notably, the van der Waals equation of state, are often implemented when the gas isn't "ideal."

Answer: Water expands when heated

Concentration of a solution can be given in various ways, but one of the most common is molarity, which is computed as moles of solute dissolved divided by liters of solution. Because water usually expands when it heats, its volume increases, and therefore, molarity will decrease. The water would not evaporate at 111 degrees Fahrenheit, remember: water's vaporization point is high, 212 degrees Fahrenheit (100 degrees Celsius), due to hydrogen bonding.

Water is actually special in that, at low temperatures, it contracts when it heats up, with the breaking point at 4 degrees Celsius. This has to do with the fact that cohesion of water molecules (again, a consequence of its ability to hydrogen bond) at low temperatures actually make the water molecules closer together in liquid form than in solid form. That's also why ice is less dense than water, and floats, unlike most solids put into their liquid phases.

Answer: At higher temperatures, solids are more soluble and gases are less soluble

In solids, solubility usually increases with increasing temperature, whereas in gases, solubility usually decreases with increasing temperature. Why?

In solids, energy is required to break the bonds holding the solid particles together, so when temperature increases and heat is supplied, the solid can dissolve more easily. In gases, when temperature increases, more of the gas particles have energy enough to escape from the liquid into the atmosphere. That's why a warm can of soda tastes flat: there are fewer gas particles in the soda. It's also why increasing temperature in the oceans could spell disaster for marine life, because less oxygen can dissolve in warmer waters.

Other factors governing solubility include pressure and type of solvent. At higher pressures, only gases will dissolve better--think of it as the gas pressure pushing gas particles into solution. Solids are unaffected. A common rule in chemistry is that "like-dissolves-like." A polar solvent (one with permanent dipoles) will dissolve polar solutes, while a nonpolar solvent will dissolve nonpolar solutes. Water (polar) and oil (nonpolar) do not mix.

Answer: The equilibrium will shift toward the reactants

Enthalpy is, essentially, a measure of the internal energy stored in the bonds of a compound (there's a lot more complicated stuff to that, but for chemistry purposes, that definition suffices). A common misconception is that it requires energy to form chemical bonds; on the contrary, energy is released when bonds are formed. It takes energy to break a bond.

Thus, when more energy is put into a reaction to break the bond, than is released by new bonds forming, the net enthalpy change is positive, because more energy is stored in bonds in the product. Such a reaction is called endothermic, and because endothermic reactions absorb energy from the surroundings, they often feel cold to the touch. On the contrary, a reaction with negative change in enthalpy is exothermic, and heats up the surroundings.

So, if you put energy into the system by raising the temperature in an endothermic equilibrium, the forward reaction will speed up, since it has more energy to use. In an exothermic reaction, the opposite holds true: the backward reaction, which requires energy to create the corresponding increase in enthalpy, will happen more readily, and the equilibrium will "shift" toward the reactants. This phenomenon is often called Le Chatelier's Principle: a chemical system in equilibrium will respond to a stress in the equilibrium by shifting toward the side that relieves the stress. In exothermic reactions, heat can be considered a "product" (remember, exothermic reactions release heat to the surroundings, and feel hot). So, if heat is added, the system will work to relieve the stress by getting rid of the heat, and moving to the "left" (reactant) side.

Answer: Spontaneous

A fundamental equation of thermodynamics states that the change in Gibbs free energy is equal to the change in enthalpy, minus the product of temperature and change in entropy. Entropy is a measure of the system's disorder: the more configurations that a system can take through rotation, translation, and vibration, the greater its entropy. For example, gas particles, which are freely moving, have greater entropy than solid particles, which are usually stuck in a lattice or other network of atoms.

Gibbs free energy is the amount of useful work that can be extracted from a system, and when it's negative, a reaction can occur spontaneously at that temperature--that is to say, an external energy source isn't needed to proceed from reactants to products. A system's spontaneity is usually either driven by its enthalpy change or its entropy change. If enthalpy change is negative (an exothermic reaction), or entropy change is positive (more disordered products than reactants), then the reaction could be spontaneous. At equilibria such as between two phases (for example, the vaporization of water at 100 degrees Celsius), Gibbs free energy is 0, because both forward and reverse reactions occur spontaneously.

Answer: Activation energy

Kinetics is the study of the rate of chemical reactions, which is affected by several factors, several of which relate to the activation energy. Both endothermic and exothermic reactions have an activation energy "barrier" that must be surpassed by particles to form an "activated complex," and, from there, form the ultimate products. At higher temperatures, more particles have enough energy to surpass the barrier, so the rate increases. A common equation used to model this is the Arrhenius equation: k = Ae^(-Ea/RT). k stands for the rate constant, a measure of how fast the reaction occurs; A is a steric factor accounting for specifics like orientation of molecules and probability of a successful collision; and Ea is activation energy. A good rule of thumb is that reaction rate roughly doubles for every 10 degrees Celsius that temperature increases.

Another way to increase reaction rate is by introducing a catalyst. Catalysts are substances that aren't consumed or produced by an overall net reaction, but provide an alternate pathway with lower activation energy. For example, hydrogenation of alkynes occurs best at high pressures and temperatures, but also when palladium metal serves as a catalyst, when the hydrocarbon adsorbs to the metal's surface, and allows hydrogen to be added more easily. Enzymes are catalysts for biochemical reactions.

Answer: A voltaic (galvanic) cell

Talk about confusing: standard temperature and pressure (STP) for chemists is defined to be one atmosphere of pressure, and 0 degrees Celsius (273K). However, thermodynamic standard state, used for many branches of chemistry, uses 25 degrees Celsius (298K) as a reference value. Thus, when conditions aren't actually standard, new adjustments must be made. The Nernst equation, which calculates the potential of an electrochemical cell, is one of those.

A voltaic cell (also called galvanic, in honor of Luigi Galvani) consists of two compartments, an anode and a cathode. At the anode, a substance loses electrons in a process called oxidation--for example, chloride ions (Cl-) could be oxidized to chlorine gas (Cl2) by losing electrons. At the cathode, the opposite occurs: a substance gains electrons, in a reduction reaction. The electrons lost by the anode travel through a wire to the cathode, forming a circuit, with a voltage across the entire contraption. Sound familiar? It's exactly what happens in a battery, just with only one cell rather than many cells.

The voltage produced by a single "half-reaction" is assigned a reference value called a reduction potential, given by the voltage produced when the half-reaction is connected to a standard hydrogen electrode (assigned a value of 0V). The overall cell's voltage is equal to the difference in the half-reaction reduction potentials that gives a positive answer. However, at non-standard states, the cell potential E is given by the Nernst equation. E = E0 - RT/nF*lnQ. E0 is the standard reduction potential at 25 degrees Celsius and one molar concentration of all species. n is the number of moles of electrons transferred in the overall reaction, F is Faraday's constant (96500 Coulombs/mole electrons), and Q is the reaction quotient, which measures the relative concentration of the species in each cell chamber.