CHEMISTRY COMMUNITY

J_CHEN 4I

Use the equation Ecell = E(cathode) - E(anode). Plug the cell potentials of the half-reactions so that Ecell > 0. When Ecell > 0, then you know what the reduction and oxidation half-reactions are by looking at the equation.

J_CHEN 4I

The units of the rate is M/s^-1 (concentration/time). For a first-order reaction, rate = k[A]^1. To make the rate be in units of M/s^-1, k must be s^-1 (remember that the unit of [A] is M).

J_CHEN 4I

Is the slow step of an overall reaction determined experimentally? Can you know what the slow step is by looking at its chemical reaction?

J_CHEN 4I

Are we supposed to know certain molecules and compounds for the final?

J_CHEN 4I

If the cell potential is not given, then assume the right is the cathode and the left is the anode. You might have to look up the cell potentials and add them up to give a positive standard cell potential to determine the anode and cathode.

J_CHEN 4I

I read the textbook and take notes, then do sapling problems, and then do the textbook problems listed on the syllabus.

J_CHEN 4I

n is the number of electrons transferred in the reaction. Unless the number of e- transferred are clear from the reaction, you can always find the number of e- by balancing the half-reactions.

J_CHEN 4I

Multiply the reaction(s) so that the number of e- are the same.

J_CHEN 4I

Q is [Products]/[Reactants] so it depends on the chemical equation.

J_CHEN 4I

How does the Gibbs free energy relate to K and Q?

J_CHEN 4I

The instantaneous rate is for finding the entire area under the curve, while the average rate gives an approximation.

J_CHEN 4I

Notice the Br2(l) is both the oxidizing and reducing agent. Therefore, you have two half-reactions: Br2(l) -> BrCO3-(aq) and Br2(l) -> Br-(aq). To balance Br2(l) -> Br-(aq), all you need to is balance Br-. For Br2(l) -> BrCO3-(aq), notice the oxygen. You need to add H2O and H+ to balance this half-r...

J_CHEN 4I

Can all the gibbs free energy equations be used for electrochemistry problems?

J_CHEN 4I

From what I remember, only thermodynamics and electrochemistry.

J_CHEN 4I

Unless the standard cell potential is given, we will probably need to look it up from a table. A lot of electrochemistry questions need the standard cell potential.

J_CHEN 4I

In acidic solutions, balance the half equation with H+ and H20. For basic solutions, balance the half reaction with OH- and H20. For some cases, like the reaction (H+) + (OH-) -> H20, you might need to look for the reduction/oxidation potentials given in the book.

J_CHEN 4I

Work is done in an electrochemical cell when electrons move across a circuit from the anode to the cathode.

J_CHEN 4I

How do you find the pH of solution using the Nernst equation? I read the chapter on it, but it is unclear to me.

J_CHEN 4I

The oxidation reaction (e.g. Zn ---> (Zn^2+) + (2 e^-) in the cell diagram Zn|Zn^2+||Cu^2+|Cu) in the anode releases electrons that flow via a circuit to the cathode where the reduction reaction ((Cu^2+) + (2 e^-) ---> Cu in the cell diagram Zn|Zn^2+||Cu^2+|Cu) takes place.

J_CHEN 4I

The "redox" in "redox reaction" is short for reduction-oxidation. The half-reaction of a reduction-oxidation reaction is the reduction reaction and the other half-reaction is the oxidation reaction.

J_CHEN 4I

Standard conditions are when the gases involved are at 1 bar, the participating solutes are at 1 mol L^-1 (1 M), and the liquids and solids involved are pure. The temperature is usually 298K.

J_CHEN 4I

A reaction is reversible when there is an infinitely small change in a variable (e.g. pressure) that changes the reaction back to its original state.

J_CHEN 4I

For this class, I don't think we really need to derive most equations since we haven't done so so far. However, for the van't Hoff equation we need understand it usage.

J_CHEN 4I

The only types of work we need to know for thermodynamics are expansion work and non-expansion work, which involve volume change.

J_CHEN 4I

Thermodynamics are relevant in biological processes that need to use energy, like photosynthesis (an endothermic reaction). There is also complicated research on entropy and its relationship to the evolution of life.

J_CHEN 4I

Another example is the autoprotolysis of ammonia (NH3). The reaction is 2NH3 (l) <-> NH4+ (aq) + NH2- (aq)

J_CHEN 4I

The heat supplied to the system is equivalent to the energy leaving the system as work.

J_CHEN 4I

For a gas (g) and solutes in solutions (aq), their activity is included for solving for K. For pure solids (s) and liquids (l), their activities are 1.

J_CHEN 4I

Delta S (sys) is the entropy of the system, Delta S (surr) is the entropy of the surroundings. Delta S (sys) + Delta S (surr) = Delta S(total), where Delta S (total) is the total entropy of both the surroundings and the system.

J_CHEN 4I

Specific heat capacity is needed because certain things require more energy to raise its temperature than other things.

J_CHEN 4I

You can write down the information given (e.g. m = 6782 g, T 53 K, q = 6783 J,...) and see what you can do with them to get to where the question is asking of you.

J_CHEN 4I

Usually, the question will tell you that the reaction is happening in a vacuum. Other than that, a keyword for knowing that a system is a vacuum is if the system is outer space.

J_CHEN 4I

Ka is for acids, so the equation would have [H3O+]. Kb is for bases, so the equation would have [OH-].

J_CHEN 4I

You first set up the equation (heat lost by the copper) = -(heat gained by the water), which is q = -q. Therefore, you are solving m*C*(T(final) - T(initial)) = - m*C*(T(final) - T(initial)). You have all the values execpt T(final).

J_CHEN 4I

delta U = 0 for isothermal expansion or compression of an ideal gas. delta U = 0, when q = 0 and w = 0 (since delta U = 0 + 0 = 0). q = -w when delta U = 0, then 0 = q + w, which is q = -w.

J_CHEN 4I

The total entropy of a system either increases or stays constant, but never decreases. Entropy is always increasing in the universe until thermodynamic equilibrium (look up "the heat death of the universe").

J_CHEN 4I

You can list all bonds on the reactant's side and the product's side, and then see if there are bonds on the product side that are not featured in the reactant side (the bonds formed) and then see if there are bonds that appeared in the reactant side but no longer appear in the product side (the bon...

J_CHEN 4I

An open system allows matter and energy to leave (or enter). For example, a cup of tea would be an open system because matter is leaving (i.e. water in the form of gas) and energy is leaving (i.e. the heat is leaving from the tea into the surroundings). A closed system does not allow matter to leave...

J_CHEN 4I

Phase changes are relevant for problems that want the enthalpy. That is because the energy needed to be supplied for a phase change in a substance is different depending on the current phase of a substance. For example, the energy needed to change a liquid to a gas (the enthalpy of vaporization) is ...

J_CHEN 4I

Since deltaH = H_final - H_initial and if the reaction is exothermic (heat is released into the surroundings), then H_final < H_initial (e.g. 3 kJ/mol - 4 kj/mol = -1 kJ/mol) which would yield a negative deltaH.

J_CHEN 4I

The pressure in an open beaker would be the pressure of the surroundings. The surroundings is typically at a constant pressure.

J_CHEN 4I

Plug the final temperature into the equation and if mCdeltaT = -mCdeltaT is true, then the final temperatures are the same.

J_CHEN 4I

Use the constant that includes the unit that is the same as the P in PV=nRT (so units cancel out nicely).

J_CHEN 4I

If the conjugate base of an acid is very stable, the reaction would favor the production of the conjugate base. If the conjugate base of an acid is not very stable, then the production of the conjugate base is not favored. This hints at the acid being weak. Same idea with bases and their conjugate a...

J_CHEN 4I

Giving pH or pOH, then [H3O+] = 10^(-pH) and [OH-] = 10^(-pOH).

J_CHEN 4I

Steam causes burns worst than water because the phase change from liquid to gases requires more energy

J_CHEN 4I

A state function is a property that does not depend on the path taken. An example of a state function is temperature. For example, a pot of boiling water at 212 F could be boiled for hours or minutes, in a microwave or an oven, etc., it would still be at 212 F. The path taken does not matter. You mo...

J_CHEN 4I

How does pressure and temperature shift a reaction?

J_CHEN 4I

Why is the value of an exothermic reaction negative and why is the value of an endothermic reaction positive?

J_CHEN 4I

Will Test 1 include any questions on ideal gases?

J_CHEN 4I

Acids and bases in solution are examples of chemical equilibria. pH and pOH are measures of the molar concentration of H3O+ and OH- in a solution respectively.

J_CHEN 4I

Professor Lavalle gave a great analogy about approximations. Basically, let's you have 1,000,000 dollars and you subtract it by x amount. If x is very small, like 10 dollars, then x is negligible because 1,000,000 - 10 = 999,990, which is almost the same as 1,000,000. In acids and bases, a weak acid...

J_CHEN 4I

Why is it that in chemical equilibria there is typically a greater concentration (or partial pressure) on one side of the reaction?

J_CHEN 4I

In lecture, the professor went over a question involving the reaction $CH_{3}COOH(aq) + H_{2}O(l)\leftrightharpoons CHCOO^{-}(aq) + H_{3}O^{+}(aq)$ and used the ICE table. Why is the intial value of H₂O zero and not 10^-7?

Search found 54 matches