Search found 27 matches

by Jiun Yue Chung 2I
Sun Mar 11, 2018 11:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K and K'
Replies: 4
Views: 167

Re: K and K'

k' (rate constant prime) is simply the 'reverse' of k (the rate constant). This means that k' is the rate constant for the reaction of products going back to the reactants.
by Jiun Yue Chung 2I
Sun Mar 11, 2018 11:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate constant
Replies: 6
Views: 214

Re: Rate constant

The rate constant is deemed a constant for a specific reaction at a specific, constant temperature. This differs from reaction rate because the rate of reaction is the speed in which a reaction is occurring. A good way to think about it is that concentration increasing or decreasing may change the r...
by Jiun Yue Chung 2I
Sun Mar 11, 2018 11:09 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 5
Views: 344

Re: Midterm 4a

I think you can identify it as irreversible because for that question, it says the external pressure is constant. For reversible changes, however, external pressure is ever so slightly changing.
by Jiun Yue Chung 2I
Sun Mar 04, 2018 11:10 pm
Forum: First Order Reactions
Topic: First order
Replies: 4
Views: 208

Re: First order

Generally if the concentration of a reactant doubles along with the reation's initial rate, it should be first order reaction. However, always do the arithmetic just to be sure :)
by Jiun Yue Chung 2I
Sun Mar 04, 2018 11:07 pm
Forum: General Rate Laws
Topic: Units for Rate Laws 15.3
Replies: 2
Views: 117

Re: Units for Rate Laws 15.3

I'm not sure what you meant by "here". However, the units for zero order reactions are (mol/L^-1 x (time unit)), for first order reactions is (time unit)^-1, and for second order reactions is (L x mol^-1 x (time unit)^-1).
by Jiun Yue Chung 2I
Sun Mar 04, 2018 11:02 pm
Forum: General Rate Laws
Topic: general rate laws
Replies: 3
Views: 150

Re: general rate laws

That's a good model to write rate laws after. But remember that some rate laws may omit some reactants and of course, the exponents (in this case m,n, and l) will be different. :)
by Jiun Yue Chung 2I
Sun Feb 25, 2018 5:04 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial rates
Replies: 5
Views: 237

Re: Initial rates

Also, there may be scenarios where your products are gases and they escape such that the only thing you can accurately rely on to calculate the rate is the reactants themselves.
by Jiun Yue Chung 2I
Sun Feb 25, 2018 4:58 pm
Forum: General Rate Laws
Topic: Writing the Rate Law
Replies: 3
Views: 143

Re: Writing the Rate Law

I don't think we do, especially since rate laws simply deal with the concentrations of substances
by Jiun Yue Chung 2I
Sun Feb 25, 2018 4:55 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Instantaneous Rate
Replies: 4
Views: 260

Re: Instantaneous Rate

We aren't just looking at initial (or at least I don't think so). There are two different equations we use to find the initial rate and then we use the Integrated Rate Laws to find rates after the start of the reaction :)
by Jiun Yue Chung 2I
Sun Feb 18, 2018 9:11 pm
Forum: Balancing Redox Reactions
Topic: "Rules"
Replies: 7
Views: 288

Re: "Rules"

In order to balance half-reactions, you often want to balance the O atoms in each first, which requires adding H2O on the other side of the equation. For instance, the half-reaction MnO4- -----> MnO2 has 4 O atoms on the left and 2 O atoms on the right. To balance, you add 2 H2O molecules to the rig...
by Jiun Yue Chung 2I
Sun Feb 18, 2018 9:00 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum electrodes
Replies: 4
Views: 175

Re: Platinum electrodes

Since Platinum is an inert metallic compound, it doesn't affect the cell reaction. Moreover, Platinum is a good electric conductor, so I guess it's often used in this redox reactions.
by Jiun Yue Chung 2I
Sun Feb 18, 2018 8:08 pm
Forum: Balancing Redox Reactions
Topic: Add H+ or OH-
Replies: 2
Views: 128

Re: Add H+ or OH-

You add H+ ions to redox reactions in acidic solution and OH- ions to redox reactions in basic solutions.
by Jiun Yue Chung 2I
Sun Feb 11, 2018 11:14 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Second Law
Replies: 2
Views: 142

Re: Second Law

If you look at example 9.1, it tells you that you can use that same equation to calculate the change in entropy when a system is being heated (reversibly). So if the question says that at constant temperature, a system is gaining some amount of energy in joules, it should be safe to use this formula.
by Jiun Yue Chung 2I
Sun Feb 11, 2018 11:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Stability and deltaG
Replies: 2
Views: 129

Re: Stability and deltaG

I think that if delta G is negative, the reaction is indeed spontaneous leading to the products being at a more stable energy state than the reactants.
by Jiun Yue Chung 2I
Sun Feb 11, 2018 11:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp v. Cv!
Replies: 5
Views: 267

Re: Cp v. Cv!

I remember from going to the midterm review session that unless the question specifically says at constant pressure, to assume using constant volume heat capacity. I think inuitively, however, that Cv should be used in the first question since yes, the pressure is the one that is changing. The secon...
by Jiun Yue Chung 2I
Mon Feb 05, 2018 1:05 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy question [ENDORSED]
Replies: 2
Views: 110

Entropy question [ENDORSED]

I remember from discussion last week and hearing about the fact that entropy is always increasing in the universe. How is this so?
by Jiun Yue Chung 2I
Mon Feb 05, 2018 12:46 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Constant K and reaction quotient
Replies: 3
Views: 147

Re: Constant K and reaction quotient

To add, K, the equilibirum constant determines the relative concentrations (and partial pressures) of the products and reactants of the reaction at equilibrium while the Q, or reaction quotient says the same thing but when the reaction is not at equilibrium. A large K indicates that the concentratio...
by Jiun Yue Chung 2I
Sun Feb 04, 2018 10:17 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sig Figs
Replies: 6
Views: 157

Re: Sig Figs

I'm sure sig figs are important when doing the calculations in the textbook.
by Jiun Yue Chung 2I
Sun Jan 28, 2018 11:47 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Adiabatic system [ENDORSED]
Replies: 1
Views: 138

Re: Adiabatic system [ENDORSED]

An adiabatic system is one where heat and matter does not flow in or outside of the system itself. A great example of an adiabatic system is a thermal container that is closed (kind of like a really good thermos). This means that if the internal energy of the system were to change in some way, then ...
by Jiun Yue Chung 2I
Sun Jan 28, 2018 11:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.41
Replies: 3
Views: 156

Re: 8.41

The way I would approach this problem is to see it in steps. First, you have to calculate the heat (q) released when the ice is melted and then calculate heat from the water changing its temperature in response to the ice cube's presence. After identifying the information you're given, you know that...
by Jiun Yue Chung 2I
Sun Jan 28, 2018 10:24 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: entropy and spontaneity
Replies: 1
Views: 114

Re: entropy and spontaneity

I think that a good way to think about this concept is to remember the picture of the gas contained in a flask (blocked by a valve that prevents it from diffusing to the rest of the flask). When you open the valve, the gas diffuses out into the rest of the flask and therefore, entropy has increased ...
by Jiun Yue Chung 2I
Sun Jan 21, 2018 3:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.115
Replies: 2
Views: 135

Re: 8.115

You could do final minus initial, but that would give you a negative change in moles. The question is asking how much H2 was burned, which already implies that the system is losing X amount of moles. The answer is positive because you wouldn't say -X moles of H2 was burned, but rather that X moles o...
by Jiun Yue Chung 2I
Sun Jan 21, 2018 3:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: How to calculate bond enthalpy
Replies: 1
Views: 214

Re: How to calculate bond enthalpy

Bond enthalpy calculation is reactant minus products because if you think about it, bond enthalpy is defined as the energy it takes to break 1 mol of a bond. Using this, positive values would be given to broken bonds (in the reactants) and negative values for bonds formed. Technically, enthalpy of r...
by Jiun Yue Chung 2I
Sun Jan 21, 2018 2:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Example 8.13
Replies: 1
Views: 104

Re: Textbook Example 8.13

I couldn't find the bond enthalpy of a Br-Br bond, so I just followed the enthalpy given on the example. After identifying the bonds broken and formed in the reaction as shown, you basically calculate the regular enthalpy of reaction using bond enthalpies. I'm not sure if you had stopped there (whic...
by Jiun Yue Chung 2I
Sat Jan 13, 2018 11:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpy vs. Bond Dissociation Enthalpy
Replies: 3
Views: 126

Re: Bond Enthalpy vs. Bond Dissociation Enthalpy

I believe there is a difference between the two. Bond enthalpy refers to the amount of energy it takes to break one mole of a bond. On the other hand, Bond Dissociation Enthalpy is referring to the enthalpy change as two atoms that were previously bonded retain the electron they put into the bond in...
by Jiun Yue Chung 2I
Sat Jan 13, 2018 10:56 pm
Forum: Phase Changes & Related Calculations
Topic: Extensive/Intensive
Replies: 5
Views: 274

Re: Extensive/Intensive

All the replies above are pretty accurate. I also think it's important not to get mixed up between chemical properties and physical ones. Just remember that intensive and extensive properties are just like sub-categories of physical properties too (that is because properties like color, mass, and vo...
by Jiun Yue Chung 2I
Sat Jan 13, 2018 6:01 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs irreversible
Replies: 2
Views: 136

Re: Reversible vs irreversible

I believe the reason why reversible processes can output the maximum amount of work is, if you recall, a reversible process must be done slowly and this causes the system to lose energy as heat much less than an irreversible process. Irreversible processes tend to be done more quickly and therefore ...

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