## Search found 50 matches

Tue Mar 10, 2020 9:43 pm
Forum: General Rate Laws
Topic: Determining Rate Laws
Replies: 4
Views: 76

### Determining Rate Laws

Can we only use the coefficients of the reactants/products in a reaction as the exponents in a rate law for intermediate rate laws?
Tue Mar 10, 2020 9:42 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics
Replies: 9
Views: 155

### Re: kinetics

A reaction that is thermodynamically favored but doesn't occur spontaneously because of a high activation energy is kinetically trapped.
Tue Mar 10, 2020 9:37 pm
Forum: First Order Reactions
Topic: Equilibrium constant and elementary reaction rate constants
Replies: 5
Views: 60

### Re: Equilibrium constant and elementary reaction rate constants

The eq constant K = kf/kr.
Tue Mar 10, 2020 9:36 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: #7.11
Replies: 2
Views: 75

### #7.11

For 7.11, how can we determine which is the rate determining step?
Tue Mar 10, 2020 9:34 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7E.3
Replies: 1
Views: 53

### Re: 7E.3

For 7E.3, we have to use a ratio of the Arrhenius equation, one at which the activation energy is 125 kJ/mol, and one at which it is 75kJ/mol. 7E.1 takes a different approach, as it says that the reverse and forward reactions rates increase using a catalyst.
Sun Mar 08, 2020 10:38 pm
Forum: General Rate Laws
Topic: Changing the mass of electrodes
Replies: 6
Views: 58

### Re: Changing the mass of electrodes

If the mass of the anode was halved, this would not affect the Ecell value, because the concentration would remain the same.
Sun Mar 08, 2020 10:36 pm
Forum: General Rate Laws
Topic: 7B5a
Replies: 1
Views: 22

### Re: 7B5a

0.693/(3.7*10^-5) = 18729.73 s
To get this in hours, we have to divide it by 3600s, to get 5.2 hours.
Sun Mar 08, 2020 10:34 pm
Forum: General Rate Laws
Topic: 7A.7 Units of Rate Constants
Replies: 2
Views: 47

### Re: 7A.7 Units of Rate Constants

The units of rate constants are based off the general rate laws for each order.
For example, zero order: rate = k*(A0)^0
Sun Mar 08, 2020 10:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate determining step
Replies: 2
Views: 43

### Rate determining step

How do we determine the rate-determining step of a reaction?
Sun Mar 08, 2020 10:31 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: order
Replies: 4
Views: 115

### Re: order

The order of a reaction is the sum of the individual orders of the reactants.
Sun Mar 08, 2020 10:29 pm
Forum: General Rate Laws
Topic: Effect on rxn rate
Replies: 2
Views: 27

### Re: Effect on rxn rate

This depends on the order of the reactant. If the order is 1, and the concentration is doubled, the overall rate doubles. If the order is 2, however, the overall rate would quadruple.
Sun Mar 08, 2020 10:28 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Speed of a reaction
Replies: 2
Views: 45

### Speed of a reaction

How do we determine of a certain reaction is slow or fast in 7C?
Sun Mar 08, 2020 10:27 pm
Forum: General Rate Laws
Topic: 7A.15
Replies: 2
Views: 44

### Re: 7A.15

We divide by the experiments where the 2 other reactions have constant concentrations. For example, to find the concentration of C, divide Exp1 by Exp 4.
Sun Mar 08, 2020 10:26 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A
Replies: 8
Views: 55

### Re: A

A is the concentration, while A0 is the initial concentration.
Sun Mar 08, 2020 10:23 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Intermediate Species
Replies: 9
Views: 127

### Re: Intermediate Species

An intermediate species is a species that plays a role in a reaction but does not appear in chemical equations for the overall reaction.
Sun Mar 08, 2020 10:22 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: molecularity
Replies: 5
Views: 32

### Re: molecularity

Termolecularity was discussed in class, but stated to be less common and unlikely.
Sun Mar 08, 2020 10:21 pm
Forum: General Rate Laws
Topic: 7A.9
Replies: 5
Views: 65

### Re: 7A.9

Convert dinitrogen pentoxide to moles, and then divide by the volume to get the molarity of N2O5. Plug this into the first order rate reaction.
Sun Mar 08, 2020 10:18 pm
Forum: General Rate Laws
Topic: Rate constant vs. rate
Replies: 4
Views: 56

### Re: Rate constant vs. rate

The rate constant of a reaction is constant. The rate of the reaction depends on the rate constant and initial concentrations of species.
Sun Mar 08, 2020 10:17 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Laws
Replies: 3
Views: 47

### Rate Laws

Can you determine the order of the rate laws solely upon inspection?
Sun Mar 08, 2020 10:16 pm
Forum: First Order Reactions
Topic: 7B.3
Replies: 2
Views: 52

### Re: 7B.3

To find the concentration of A, you multiply (2molA/1molB) * (.034molB./L) to get 0.068 mol. Subtract this from the initial 0.153 to get 0.085
Sun Mar 08, 2020 10:13 pm
Forum: Second Order Reactions
Topic: half life
Replies: 6
Views: 40

### Re: half life

First order reaction: t0.5 = 0.693/k
Second order reaction: t0.5 = 1/(k * A0)
Sun Mar 08, 2020 10:12 pm
Forum: Balancing Redox Reactions
Topic: Why do we flip E for oxidation?
Replies: 13
Views: 111

### Re: Why do we flip E for oxidation?

In the appendix, the equations are given as reductions. So, for the E for oxidation, we flip the reaction and change the sign of E.
Sun Mar 08, 2020 10:11 pm
Forum: General Rate Laws
Topic: Rate limiting step
Replies: 12
Views: 128

### Re: Rate limiting step

The slowest step of the elementary reactions is called the rate limiting step.
Sun Mar 08, 2020 10:10 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity and rate laws
Replies: 5
Views: 83

### Re: Molecularity and rate laws

Molecularity corresponds directly to the order of the reaction. (unimolecular = 1, bimolecular = 2, etc)
Sun Mar 08, 2020 10:09 pm
Forum: General Rate Laws
Topic: units
Replies: 12
Views: 120

### Re: units

the rate constant k has units s-1 for a first order reaction, and (L*mol-1*s-1) for a second order reaction.
Sun Feb 09, 2020 10:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat is enthalpy or Q?
Replies: 2
Views: 36

### Re: Heat is enthalpy or Q?

At a constant pressure, q and delta H are interchangeable.
Sun Feb 09, 2020 10:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A11
Replies: 3
Views: 56

### Re: 4A11

The q value given is 22.5, not 25. So:
Ccal=22.5kJ/(23.97-22.45) + 14.8026
Sun Feb 09, 2020 10:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: reversible reactions
Replies: 4
Views: 47

### Re: reversible reactions

I believe the question states it if its reversible, which is the only scenario where we'd use the reversible reaction equation for W.
Sun Feb 09, 2020 10:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: H and Q
Replies: 4
Views: 113

### Re: H and Q

delta H is equal to Q when the system has a constant pressure, and no nonexpansion work.
Sun Feb 09, 2020 10:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: work on the system or by the system
Replies: 4
Views: 42

### Re: work on the system or by the system

W is positive if work is done by the system, and it's negative if work is done on the system.
Sun Feb 02, 2020 11:23 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Types of Systems
Replies: 7
Views: 162

### Re: Types of Systems

A closed system can be changed through heat transfer and work only, while an open system can allow for energy and matter exchange.
Sun Feb 02, 2020 11:22 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Changing a Closed System
Replies: 2
Views: 23

### Re: Changing a Closed System

A close system can be changed through heat transfer and work.
Sun Feb 02, 2020 11:21 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Changing the energy of a system
Replies: 9
Views: 74

### Re: Changing the energy of a system

The energy of a system can be changed through heat, work, and mass flow.
Sun Feb 02, 2020 11:20 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Enthalpy of formation vs. heat capacity
Replies: 2
Views: 32

### Re: Enthalpy of formation vs. heat capacity

Specific heat capacity is the amount of energy needed to raise the temperature of 1g of a substance by 1C. The standard enthalpy of formation, however, is the change in enthalpy when one mole of a substance is formed from its pure elements.
Sun Feb 02, 2020 11:11 pm
Forum: Calculating Work of Expansion
Topic: reversible expansion
Replies: 6
Views: 51

### Re: reversible expansion

A process is reversible if an extremely small change can reverse it. For example, an extremely small increase in pressure can move an object into a container, while an extremely small decrease in pressure can push the object out. No change in pressure won't move the object.
Sun Jan 26, 2020 10:43 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Finding Ka from pH
Replies: 5
Views: 60

### Re: Finding Ka from pH

[H3O+] = 10^(-pH) and [OH-] = 10^(-pOH), and you can plug these values into the equations for Ka and Kb: Ka = ([H+][A-]/[HA])
Sun Jan 26, 2020 10:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpies of Formation
Replies: 4
Views: 31

### Re: Standard Enthalpies of Formation

The standard enthalpy of formation is a measure of the energy consumed or released when a substance is created under standard conditions, and can be calculated.
Sun Jan 26, 2020 10:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE
Replies: 20
Views: 187

### Re: ICE

ICE tables are used when you're looking for the equilibrium concentration of a certain reactant or product, and are given the initial concentration. With an ICE table, using a quadratic formula, you can easily solve for the given concentration.
Sun Jan 26, 2020 10:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changing K
Replies: 13
Views: 116

### Re: Changing K

K is changed by temperature, but not pressure or adding/removing reagents/compression.
Sun Jan 26, 2020 10:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Reaction Enthalpies
Replies: 2
Views: 31

### Standard Reaction Enthalpies

How do we calculate the standard reaction enthalpy if bond enthalpies aren't given?
Sun Jan 26, 2020 10:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Reaction Enthalpies
Replies: 2
Views: 23

### Standard Reaction Enthalpies

For standard reaction enthalpies, does it matter that reactants and products can be in different states, and do we have to differentiate between them?
Sun Jan 26, 2020 10:26 pm
Forum: Phase Changes & Related Calculations
Topic: Hess's Law
Replies: 8
Views: 66

### Re: Hess's Law

Hess's Law is a law that says that the total enthalpy change for a reaction is the sum of all changes in it.
Sun Jan 26, 2020 10:25 pm
Forum: Phase Changes & Related Calculations
Topic: delta H
Replies: 3
Views: 31

### Re: delta H

The reaction enthalpy is the the enthalpy difference between the reactants and products, while the enthalpy of formation is the enthalpy change when a substance in the standard state is formed from its pure elements.
Sun Jan 26, 2020 10:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard State
Replies: 2
Views: 34

### Re: Standard State

The standard state of a molecule is given by its phase at 25 degrees Celsius, and 1 atm. Mercury and Bromine are liquid, while the noble gases and H, O, and N are gases. The rest of the elements are solid.
Sun Jan 19, 2020 8:00 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw question
Replies: 2
Views: 21

### Re: Kw question

At equilibrium, pure water at 25 C contains 1.0 x 10-7 moles per liter of H3O+ and OH-.
Sun Jan 12, 2020 7:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Thinking point 5J
Replies: 4
Views: 46

### Re: Thinking point 5J

Because solids are not included in the equilibrium expression, removing it would not affect the equilibrium constant.
Sun Jan 12, 2020 7:09 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: increasing N2
Replies: 5
Views: 96

### Re: increasing N2

This is because increasing N2 would lead to the forward reaction being favored, increasing the concentration of NH3, and decreasing the concentration of H2.
Sun Jan 12, 2020 7:05 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Equilibrium Concentrations using I and K
Replies: 3
Views: 38

### Re: Equilibrium Concentrations using I and K

You could solve for concentration of the product by using a RICE - Reactants, Initial, Change in Concentration, Equilibrium Concentration table, and leaving (x) as the concentration of the product. You would plug in the initial concentrations, and the equilibrium constant into the algebraic expressi...
Sun Jan 12, 2020 7:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert gas
Replies: 6
Views: 61

### Re: Inert gas

Adding an inert gas affects pressure, but not the individual partial pressures of the gasses. So, the Kp remains constant, and the reaction isn't shifted.
Sun Jan 12, 2020 7:01 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: volume change with inert gas
Replies: 9
Views: 100

### Re: volume change with inert gas

The reaction doesn't shift because although the pressure does increase, the partial pressures of the existing gasses aren't affected by adding an inert gas.