Search found 44 matches

by shaunajava2e
Thu Jan 31, 2019 2:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: understanding calculating reaction enthalpy
Replies: 2
Views: 17

Re: understanding calculating reaction enthalpy

The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions.
by shaunajava2e
Thu Jan 31, 2019 2:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy
Replies: 4
Views: 27

Re: Standard Enthalpy

All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.
by shaunajava2e
Thu Jan 31, 2019 2:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Isolated systems
Replies: 10
Views: 39

Re: Isolated systems

An isolated system is a thermodynamic system that cannot exchange either energy or matter outside the boundaries of the system. An isolated system differs from a closed system by the transfer of energy. Closed systems are only closed to matter, energy can be exchanged across the system's boundaries.
by shaunajava2e
Thu Jan 31, 2019 2:41 pm
Forum: Ideal Gases
Topic: breaking bond - heat released and gained
Replies: 4
Views: 21

Re: breaking bond - heat released and gained

Breaking Bonds Requires Energy. You have to put energy into a molecule to break its chemical bonds. The amount needed is called the bond energy.
by shaunajava2e
Thu Jan 31, 2019 2:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework
Replies: 9
Views: 48

Re: Homework

a lot of the questions tend to jump around if you're following what we learn in class, but by the end of the chapter we usually have covered all the topics
by shaunajava2e
Thu Jan 31, 2019 2:39 pm
Forum: Ideal Gases
Topic: atm vs. bar?
Replies: 17
Views: 108

Re: atm vs. bar?

they are both units of measurement for pressure and depending on your TA, both should be fine to use
by shaunajava2e
Wed Jan 16, 2019 10:22 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic vs. Endothermic Reaction
Replies: 9
Views: 41

Re: Exothermic vs. Endothermic Reaction

A quick difference between endothermic and exothermic involves reactions in the environment. An endothermic reaction takes place when energy is absorbed from surroundings in the form of heat, and exothermic is when energy is released from the system into the surroundings.
by shaunajava2e
Wed Jan 16, 2019 10:20 am
Forum: Ideal Gases
Topic: Homework for week 2 [ENDORSED]
Replies: 10
Views: 93

Re: Homework for week 2 [ENDORSED]

week two can be either outline 1 or 2
by shaunajava2e
Wed Jan 09, 2019 1:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What does it mean when a reaction is at equilibrium?
Replies: 4
Views: 25

Re: What does it mean when a reaction is at equilibrium?

the rates of product changing to reactants and reactants changing to products are the same
by shaunajava2e
Wed Jan 09, 2019 1:06 pm
Forum: Ideal Gases
Topic: Q and K [ENDORSED]
Replies: 35
Views: 780

Re: Q and K [ENDORSED]

the formulas are the same, K is at equillibrium
by shaunajava2e
Wed Jan 09, 2019 10:15 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

You must be full of copper and tellurium because you're CuTe!
by shaunajava2e
Fri Dec 07, 2018 3:00 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

The best thing about learning equilibrium is that nothing changes.
by shaunajava2e
Fri Dec 07, 2018 3:00 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

Don't tell jokes to noble gases you'll get no reaction.
by shaunajava2e
Thu Nov 08, 2018 11:53 am
Forum: Lewis Structures
Topic: Octet rule question
Replies: 6
Views: 98

Re: Octet rule question

elements in the 3rd period and onwards are able to take advantage of their empty d orbital and expand their octet past the 8 electrons that come with the p and s orbitals.
by shaunajava2e
Thu Nov 08, 2018 11:43 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

all the good chemistry jokes Argon, i think we should take the bad ones and Barium.
by shaunajava2e
Thu Nov 08, 2018 11:41 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

!!
by shaunajava2e
Thu Nov 08, 2018 11:40 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 6981
Views: 771017

Re: Post All Chemistry Jokes Here

what is the chemical formula for a banana?
BaNa2
by shaunajava2e
Thu Nov 08, 2018 11:37 am
Forum: Bond Lengths & Energies
Topic: bond lengths and strengths
Replies: 9
Views: 88

Re: bond lengths and strengths

the longer the bong the weaker it is, this is because if the bond length is longer it is easier to break
by shaunajava2e
Thu Nov 08, 2018 11:36 am
Forum: Lewis Structures
Topic: Formal charge question
Replies: 9
Views: 100

Re: Formal charge question

if you have accounted for all the electrons and checked for everything else (like stated above,) yes, formal charge is a great way double check that your structure is in the most stable form.
by shaunajava2e
Thu Nov 08, 2018 11:34 am
Forum: Properties of Light
Topic: Exam 2 Question 4A
Replies: 6
Views: 185

Re: Exam 2 Question 4A

e=hv, like stated above should have been used, but it was also necessary to convert the units from kJ to J which could result in error as well.
by shaunajava2e
Thu Nov 08, 2018 11:31 am
Forum: Octet Exceptions
Topic: Copper
Replies: 10
Views: 118

Re: Copper

^^ the rule applies for copper and chromium and all elements under them in the 9th and 6th groups (however lavelle said in class we won't be going past the 4th period so we don't need to worry about any elements other than copper and chromium)
by shaunajava2e
Thu Nov 08, 2018 11:29 am
Forum: Bond Lengths & Energies
Topic: MIDTERM Bond Length Question
Replies: 15
Views: 157

Re: MIDTERM Bond Length Question

since there was only the two bonds, the length would be the average of their individual lengths, so the average of 140 and 120, resulting in 130
by shaunajava2e
Thu Nov 08, 2018 11:28 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 11
Views: 129

Re: Formal Charge

formal charge is very relative and dependent on the amount of valance electrons an element has in the periodic table and how many it is given in the lewis structure
by shaunajava2e
Thu Nov 08, 2018 11:26 am
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 3
Views: 33

Re: Resonance Structures

the location of a bond in a structure can be interchanged, there is a resonance structure.
in this example, the double bond can be written on either side and therefore there is resonance
by shaunajava2e
Thu Nov 08, 2018 11:22 am
Forum: Lewis Structures
Topic: Formal charges
Replies: 15
Views: 105

Re: Formal charges

formal charges can be used to help determine the most stable lewis structure, however you dont need to explicitly state them unless the questions says so
by shaunajava2e
Thu Nov 08, 2018 11:18 am
Forum: Bond Lengths & Energies
Topic: Bond Length and Bond Strength
Replies: 5
Views: 46

Re: Bond Length and Bond Strength

thats correct! and the shorter the bond the stronger it is
by shaunajava2e
Thu Nov 08, 2018 11:18 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge & Stable lewis structures
Replies: 6
Views: 53

Re: Formal Charge & Stable lewis structures

the goal is to make the formal charge for each element 0 or as close to 0 as possible. if after calculating the formal charges of each element in the compound there are no elements with 0 formal charges, there is likely a better structure that can be shown.
by shaunajava2e
Thu Nov 08, 2018 11:15 am
Forum: Lewis Structures
Topic: Expanded octet
Replies: 4
Views: 51

Re: Expanded octet

electrons in the 3rd period and on can take advantage of their empty d orbital and use it to hold electrons and make themselves more stable by reducing their formal charge (resulting in going over the 8 that gets held by the p+s orbitals)
by shaunajava2e
Sun Oct 28, 2018 4:56 pm
Forum: Ionic & Covalent Bonds
Topic: Trend of Ionic Radii
Replies: 5
Views: 50

Re: Trend of Ionic Radii

ionic radius, atomic radius, and covalent radius all follow the same trends, increases down a group and decreases across a period, being greatest in the bottom right corner of the periodic table
by shaunajava2e
Sun Oct 28, 2018 4:52 pm
Forum: Ionic & Covalent Bonds
Topic: the Octet rule
Replies: 21
Views: 138

Re: the Octet rule

all elements follow the octet rule except hydrogen, helium, lithium, and beryllium which have a max of 2 valance electrons
by shaunajava2e
Sun Oct 28, 2018 4:49 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 8
Views: 63

Re: Lewis Structures

the number of electrons is equivalent to the amount of valance electrons the element has
by shaunajava2e
Mon Oct 22, 2018 2:18 pm
Forum: *Particle in a Box
Topic: Test 2
Replies: 9
Views: 211

Re: Test 2

reviewing whats on the quantum world outline on his website should help!
by shaunajava2e
Mon Oct 22, 2018 2:12 pm
Forum: Properties of Light
Topic: kg or g [ENDORSED]
Replies: 11
Views: 181

Re: kg or g [ENDORSED]

everything uses kg, molar mass is given in g per mole however for simplicity purposes and to make it easier to write out.
by shaunajava2e
Mon Oct 22, 2018 2:11 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: What is the equation used for?
Replies: 9
Views: 97

Re: What is the equation used for?

the equation is used to calculate the range in momentum or position of the electron as both cannot be calculated accurately at the same time. due to the way we carry out the experiment to calculate for position and momentum, we can not be certain of the values of one.
by shaunajava2e
Sat Oct 13, 2018 1:50 pm
Forum: DeBroglie Equation
Topic: De Broglie Equation Dividing J*s by kg*m/s
Replies: 2
Views: 25

Re: De Broglie Equation Dividing J*s by kg*m/s

1 J= 1 kg.m^2.s^(-2) the units in the de broglie equation are: (J.s)/(kg.m/s) this becomes: [(1 kg.m^2.s^(-2))(s)]/(kg.m/s) the kgs on both sides cancel out there is a s^(-2) and s on top, and a s on the bottom, these cancel out as well the m^2 on top cancels out with one m on the bottom to end with...
by shaunajava2e
Sat Oct 13, 2018 1:46 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Wavelike properties
Replies: 7
Views: 50

Re: Wavelike properties

wavelengths under 10^-15 or 10^-18 are so small that their wavelengths cannot be detected and therefore are said to have no wavelike properties
by shaunajava2e
Sat Oct 13, 2018 1:45 pm
Forum: DeBroglie Equation
Topic: Wavelike Properties
Replies: 2
Views: 37

Re: Wavelike Properties

everyday objects and objects that can be seen with the human eye won't have detectable wavelike properties
by shaunajava2e
Sun Oct 07, 2018 7:38 pm
Forum: Properties of Light
Topic: Chapter 1 Homework
Replies: 6
Views: 111

Re: Chapter 1 Homework

7 problems relevant to the material are due every week in your discussion section
by shaunajava2e
Sun Oct 07, 2018 7:37 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Procedure
Replies: 7
Views: 133

Re: Balancing Procedure

adding an O atom would change the composition of the molecule and therefore change the substance
by shaunajava2e
Sun Oct 07, 2018 7:36 pm
Forum: Limiting Reactant Calculations
Topic: Theoretical Yield
Replies: 7
Views: 88

Re: Theoretical Yield

due to side reactions and impurities the actual yield will often be less than the theoretical yield
by shaunajava2e
Thu Oct 04, 2018 11:54 am
Forum: Empirical & Molecular Formulas
Topic: Empirical Formula
Replies: 6
Views: 64

Re: Empirical Formula

technically you can use any mass you choose however 100g is almost always used as it reduces the amount of calculations needed and makes it simpler
by shaunajava2e
Thu Oct 04, 2018 11:49 am
Forum: Empirical & Molecular Formulas
Topic: Definition of Empirical Formula
Replies: 8
Views: 96

Re: Definition of Empirical Formula

the empirical formula simplifies the ratio of the atoms in a formula, the molecular formula shows the actual number. as a result, the empirical formula of multiple molecules could be the same while the molecular formulas cannot
by shaunajava2e
Thu Oct 04, 2018 11:44 am
Forum: Significant Figures
Topic: Sig Fig's in Problem E.21.d
Replies: 3
Views: 44

Re: Sig Fig's in Problem E.21.d

I'm assuming they are using the molar mass of H as its shown in the front cover of the book, in which case it would be 1.0079 g.mol-1 which has 5 sigfigs

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