CHEMISTRY COMMUNITY

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The reaction order is determined experimentally. Thus, the pattern is as follows: If the reactant concentration is doubled and the rate is unchanged, then the reactant is zero order. If the reactant concentration is doubled and the rate is doubled, then the reactant is first order. If the reactant c...

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Catalysts can be included in the rate law. This occurs when the catalyst is involved in the rate-determining step, since the reactants of the rate-determining step is what decides the overall rate law. However, if the catalyst is involved in a different step, then it will not appear in the rate law.

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The amine functional group is a nitrogen atom with three bonds, and one of which is the carbon atom. This means that nitrogen can form two other bonds and is not restricted to hydrogen for those bonds.

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A nucleophile is a species that will donate an electron pair to form a chemical bond. These nucleophiles can take part in substitution reactions, in which the nucleophile is attracted to a full or partial positive charge, and it serves as a replacement for a leaving group.

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A negative order means that the concentration of a species inversely affects the rate of a reaction.

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In general, at any stage of the reaction, we can find how much of a reactant is remaining after n half-lives by (1/2)^n [A]0. Thus, if 1/2 is a factor of the remaining amount, then it is allowed to use the half life method.

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Note that the equation for the formation of HI is given by: H2 + I2 → 2 HI Since the question gives that each reactant is to the first order, this means that the total order, given by the sum of individual orders for each reactant, is 1+1, or 2. A reaction need not be dependent on only one reactant ...

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The order of a reactant, n, explains more about the reaction mechanism because it directly describes how the concentration of a reactant affects the rate of the reaction. From this, the rate law can be used to calculate the reaction rate using known concentrations of reactants.

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Pseudo rate laws are useful in finding the overall rate law when a reaction has multiple reactants with changing concentrations. What this allows is to assume that the concentrations of the other reactants do not change, so the reaction appears as a first order.

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Electromotive force is the cell potential of a system. A higher potential implies that the chemical reaction provides an electric current that is sufficient enough to electrons to transfer. As a result, this means that there is no need for outside input, and the reaction is spontaneous. From this, w...

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A way to determine which species is reduced and/or oxidized is by comparing the values of standard potentials for the species. Whichever one has the more positive potential, this species is the one with greater electron-pulling power as a reduction half reaction, meaning this species is more likely ...

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Typically, when we flip the reduction half reaction so that the electrons are on the left hand side, we are required to change the sign of E°. However, when we are using the E°cell=E°cathode-E°anode, the subtraction operation already accounts for the sign switch, hence we can use the standard reduct...

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W is the number of microstates that a particular atom or molecule can take. A good way to find the value for W is to consider the form:
(number of states)^(number of particles).
This means that the base refers to the orientation of the particular atom/molecule.

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The thermodynamic stability of a molecule means that the formation is favored, so the reaction is spontaneous. The way by which we can determine spontaneity from Gibbs Free Energy is by using the equation deltaG = deltaH - TdeltaS. This allows us to compare how altering the values of the variables w...

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Heat is the transfer of energy due to a difference in temperature. On the other hand, enthalpy is the change in amount of heat in a system at constant pressure. This means that heat is a path dependent function, while enthalpy is a state function.

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A galvanic cell is simply the electrochemical cell that uses the transfer of energy in redox reactions, which supplies an electric current. It comprises of two half cells connected by a salt bridge, and the transfer of electrons is spontaneous. As a result, there will always be a positive voltage

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The half reaction would need to be balanced first, so the equation would look like H2O (l) + O3 (g) + 2e- --> O2 (g) + 2OH- (aq). As mentioned, both O3 and O2 have no charge, but since the products contains two hydroxide ions, the overall charge needs to be balanced by adding two electrons to the le...

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I believe a description of the changes in the reaction due to increase in temperature is acceptable. As mentioned, by observing that the equilibrium constant decreases, this implies increased reactant formation. As a result, this deems that there will be less ammonia formed upon heating.

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We can substitute the expressions for the heat capacities at both constant volume and pressure if we are aware of the molecular complexity. This means classifying the substance as monatomic, linear molecule, or nonlinear molecule.

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This question was simply poorly worded, because ideal conditions for a gas does not imply the number of moles. If it were standard conditions, then typically the amount of gas would ideally be 1 mol. However, ideal conditions simply pertain to abiding the ideal gas law.

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The change in molar internal energy of a monatomic ideal gas at a temperature T is (3/2)*deltaT. So, when calculating the molar heat capacity at constant volume, which is deltaU/deltaT, the quotient is (3/2)*T. Since Cv is (3/2)*T, and Cp=Cv+R, Cp=(5/2)*T. We substitute this equation in for C in the...

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Internal energy is simply the total store of energy in a system, which is associated with the random and disordered motion of molecules. On the other hand, temperature measures how much the molecules of a substance are moving. Thus, internal energy is a state function that is dependent on temperatur...

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Entropy is simply energy divided by temperature, which yields the unit of Joules per Kelvin (J)*(K^-1).

Note that another property is the entropy of a pure substance, which is given by entropy per unit amount of substance. The unit for this is given by J*(K^-1)*(mol^-1).

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A perfect crystal is a substance in which all the molecules are lined up perfectly, so there are no planar imperfections. Nothing within the crystal is moving, so the arrangement cannot be altered. This implies that at ground state, a perfect crystal would have a degeneracy of 1, or W=1; subsequentl...

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One way to determine this would be to observe if the entropy of the system increases. This is because all processes naturally seek to increase in entropy. In the case that the entropy decreases, this means that the process could not have occurred in the real world without intervention. Thus, spontan...

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An extensive property is a property that does depend on the size/extent of the sample. On the other hand, an intensive property is independent of the size of the sample. For example, volume is an extensive property and temperature is intensive. It may prove useful to know that these two are physical...

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Consider how work is equal to -P∆V. The change in volume of the pump is negative since the pump is being depressed. So algebraically, when substituting a negative value for deltaV, the sign for work will be positive, hence implying that work is being done. Conceptually, the work is positive because ...

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Delta U is the change in the internal energy of the system. In the piston model, when there is expansion energy, the system is doing work on the surroundings which causes a positive increase in volume, thus yielding w= -PΔV since the system lost energy when expanding. As a result, delta U = q-PΔV. H...

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The sign does change in a reverse reaction. The reasoning is that since enthalpy is a state function, the energy required to push a forward reaction to its products would be directly reversed to push it back to its reactants.

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Given that nitrogen dioxide formation is a multi-step reaction, this means that in order to achieve the overall reaction there will be intermediate steps. In this case, NO (g) is a product of the first reaction but a reactant of the second reaction; thus, NO acts as an intermediate, and since the am...

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Yes, given that the enthalpies are organized into a table, this means that these values must be given at a specific temperature. Hence, we can assume that the reactions will be paired with enthalpies at 25 degrees Celsius.

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Atoms with higher electronegativity will be less inclined to share its electrons with a proton. Thus, increasing electronegativity of an atom will decrease basicity, and weaker bases have stronger conjugate acids. Another way to think about this is that with increasing electronegativity, the H-A bon...

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The higher the Ka value is, the more protons are donated by the acid, which means the acid is stronger and then pKa value will be lower. Consequently, since the acid is stronger, it will also have a lower pH value. Thus, we can draw a direct relationship.

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The first equation has 2 molecules of PCl3 as product, while the second equation has 1 molecule of PCl3 as reactant. However, we notice that the third and final equation is the overall reaction, and PCl3 is neither a reactant nor product. Hence, this implies that PCl3 is an intermediate and must be ...

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You are only allowed to assume that the initial concentration/pressure of the products is equal to zero. Since the reaction proceeds only when there exists a reactant, the reactant will never have an initial concentration/pressure of zero. However, if the initial concentration/pressure of the reacta...

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Think of K as the equilibrium constant, and equilibrium is the final stage of the reaction. Thus, K describes the final concentrations of products and reactants. On the other hand, Q is simply a reaction quotient, which means the expression is a relative ratio of products and reactants at a given in...

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How does the CFT help predict the color of a coordination complex? It seems the color is drastically impacted by the ligands.

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I believe we will not need to know specific bond angles when there are lone pairs. The interaction between a lone pair and bond pair, which is a repulsion, changes the bond angle to a lower value, but we cannot be certain to what degree this change will be. As a result, all we can state is that the ...

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Yes, the lone pairs do count as an electron group towards the hybridization of the central atom since hybridization is based on electron density, which consists of the bonds and lone pairs. As for atoms with four regions of electron density, the central atom would be sp3 hybridized. Once the number ...

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An ionic bond is formed between a metal and nonmetal, and since the nonmetal is more electronegative, the nonmetal will take the electrons from the metal. This produces an electrostatic attraction between oppositely charged ions in a compound. A covalent bond is formed between two nonmetals, which i...

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Dipole moments arise from a difference in electronegativity, and the atoms in a molecule share the electrons unequally. As a result, the atoms involved in a covalent bond will gain either a partially positive or partially negative charge. This establishes a dipole that separates the charges. Dipoles...

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"H2C" is merely the same as "CH2", except the first is a way to show placement of the hydrogens. Since the bonds are not on hydrogen, it becomes easier to write it as H2C-C to show that the bonds are in fact between carbon. It may be preferable to keep your answer when writing ou...

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Given that the Cl atom already has 7 valence electrons, and 6 of those are lone pairs, the Cl atom has only one available valence electron for bonding. This means that chlorine is only able to form one bond, which means there can only be a single bond and not a double bond between N and Cl atoms. Th...

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An isomer refers to a molecule with the same molecular formula but different chemical structure, whereas a resonance structure is when more than one Lewis structure can be drawn for the molecule. The key difference between these two is that different chemical structures is a result of rearranging th...

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Typically, as the occupied energy levels increase in principle quantum number, the energies move closer together, which implies that the energy is dependent on the number of electrons in the level. However, with transition metals, this does not happen when the electrons occupy high energy levels. He...

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Yes, the zeros in 300 are not considered for significant figures but merely space holders, which gives 300 only 1 significant figure. By adding the decimal at the end, the zeros serve as additional measurement decisions which makes the zeros significant, which gives 300. 3 significant figures; note ...

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The idea is that since s-electrons do not have a node at the nucleus as opposed to p-electrons with nodes. This difference in shape allows for more electron penetration by the s-electrons. As a result, this decreases the shielding of the s-electrons, and getting closer to the nucleus adds more nucle...

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Chromium acts like an exception in the sense that 3d5 is a more stable configuration than 3d4, the reason being that an exactly half filled sub-shell is partially full is more stable than a partially sub-shell. As a result, an electron from the 4s orbital is excited and rises to the 3d orbital.

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With multi-electron atoms, they are characterized by equations used to describe wavelengths that are unique from hydrogen, so using the Rydberg formula for these atoms will yield an incorrect value. As far as I believe this class is concerned, we will only be working with the hydrogen atom as it onl...

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Since the Rydberg formula is essentially a change equation describing the change in energy from one energy level to another, one will always calculate the difference as final minus initial. This is one way to remember that in the parenthesis, n2 is the final energy level for the electron.

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Other conversions that may prove useful include:
1000mL = 1L, for volume analysis
1000 g = 1kg for mass analysis

Knowing the difference will make converting units easier when doing dimensional analysis.

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Really, all the periodic table jokes argon?
I don't zinc so.

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