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    • Thermodynamics >
      • Thermochemistry Worksheet + Answers
      • First Law of Thermodynamics
      • Pressure-Volume Work
      • Enthalpy
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      • Heat Capacity
      • Calorimetry
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      • How to Balance Redox Reactions (Basic Solution)
      • Galvanic Cells
      • Standard Reduction Potentials
      • Electrolytic Cells
      • Nernst Equation
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      • Introduction
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      • Rate Laws
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      • First-Order Reactions
      • Second-Order Reactions
      • Half-Life Expressions
      • Arrhenius Equation
      • How Long will it Take to Decay?
      • What Order is this Reaction?
      • Find the Rate Constant
    • Gases >
      • Pressure, Volume, Temperature
      • Ideal Gas Law
      • Density of Gases
      • Ideal Gas Law and Changes in P, V, T
      • Kinetic Molecular Theory
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      • Partial Pressures
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      • Clausius-Clapeyron Equation
      • Heating Curves
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      • Simple Cubic, fcc and bcc
      • How to Find Edge Length
    • Organic Reactions >
      • Br2 + Alkene (Adding across a double bond)
      • HCl + Alkene (Adding across a double bond)
      • Reaction of OH with Alkyl Halide
      • What is Regioselectivity?
    • Moles and Mass >
      • Average Atomic Mass
      • Solve for Isotopic Abundance
      • Limiting Reagents
      • Percent Yield
      • Actual Yield and Percentage Yield
      • Percent Composition
    • Atomic Structure >
      • What's in an Atom?
      • Quantum Numbers
      • Pauli, Aufbau, Hund
      • Light: E h ν λ
      • Energy Levels of Hydrogen
      • Energy Levels of Non-Hydrogen Atoms
    • Organic Naming >
      • Naming Organic Molecules
      • How to Name Amines
      • How to Name Amides
    • Lewis Structures
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Rank the compounds NH3, CH4, PH3 in order of increasing boiling point. Explain your answer.

2/2/2021

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Question from a reader: Rank the compounds NH3, CH4,PH3 in order of increasing boiling point. Explain your answer.
  • NH3 is highest because the N-H bonds give it Hydrogen Bonding Intermolecular Forces.
  • PH3 is next highest because it has dipole dipole forces, which are weaker than “hydrogen bonding"
  • CH4 has neither of those. It only has London Dispersion forces which are weak. It has the lowest boiling point of the three.
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Rank Compounds from Weakest to Strongest Intermolecular Forces based on Boiling Points

2/2/2021

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Question from a viewer: Water, H2O, boils at 100 degree Celsius ; ethanol, C2H5OH, boils at 78 degree Celsius, and ammonia NH3 boils at -33 degree Celsius. Rank these three compounds in order from weakest to strongest intramolecular interaction. Explain how you get your answer.
Higher boiling point = stronger intermolecular forces.

Water boils at a higher temperature because its hydrogen-oxygen bonds cause hydrogen bonding, which is a strong intermolecular force that makes the molecules stick to each other. This means you have to add more energy (heat) to get them to separate and boil.

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Write a Likely Formula for a Simple Compound made from ...

2/2/2021

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Question from a viewer: For each of the following pairs of atoms, write a likely formula for a simple compound made from them, and indicate if the bonding is ionic or covalent.
A) Ca & Cl
B) S& H
C) Cl & N
D) Fe & Br
Ca and Cl --> Ca is a metal, Cl is a non-metal, therefore they are IONIC together
Video of me drawing the diagram to connect the two: https://www.youtube.com/watch?v=8aDXuwsDxWE

S and H are both non-metals --> they are COVALENT together.
S brings 6 valence electrons and needs two more. H brings one each, so  you need TWO hydrogens to bond with ONE sulfur --> H2S

Cl and N are both non-metals --> they are COVALENT together.
N has 5 valence electrons and needs 3 more. Each Chlorine shares ONE and so you need THREE chlorines --> NCl3

Fe is a metal and Br is a non-metal --> they are IONIC together.
This one is tough unless you know (or have a periodic table that tells you) that Fe can have charges or either +2 or +3.
+2 charge --> FeBr2
+3 charge --> FeBr3
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What's the Difference between Molecules and Compounds?

2/2/2021

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A question from a viewer: How do we find the difference between molecules and compounds? I know that all compounds are molecules, but not all molecules are compounds, but how do we find the difference by just looking at a given atom? ex: O2, O3, CO2, etc. Thank you!
A molecule is anything made of 2 or more atoms
O2 is a molecule because it is made of 2 atoms
O3 is a molecule because it is made of 3 atoms
CO2 is a molecule because it is made of 3 atoms

A compound is anything made of 2 of more ELEMENTS
O2 is NOT a compound because it is only made of oxygen
O3 is NOT a compound because it is only made of oxygen
CO2 IS a compound because it is made of carbon and oxygen (2 different elements)
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Calculate δHrxn for the following reaction: c(s)+h2o(g)→co(g)+h2(g)

7/23/2020

1 Comment

 
One question that leads people to my website more often than any other ...

Question: Calculate δHrxn for the following reaction: c(s)+h2o(g)→co(g)+h2(g)

use the following reactions and given δh values:
c(s)+o2(g)→co2(g), δh= -393.5 kj
2co(g)+o2(g)→2co2(g), δh= -566.0 kj
2h2(g)+o2(g)→2h2o(g), δh= -483.6 kj

This is a classic Hess' Law question. Your job is to rearrange the three given reactions so that they add up to (and cancel to) the target reaction.

Keep Reaction 1 as is.
Reverse Reaction 2 and cut in half.
Reverse Reaction 3 and cut in half.

c(s)+o2(g)→co2(g), δh= -393.5 kj
co2(g)→co(g)+0.5 o2(g), δh= +283.0 kj

​h2o(g)→h2(g)+0.5 o2(g), δh= +241.8 kj
Added together:
c(s)+h2o(g)→co(g)+h2(g)
Total enthalpy: -393.5 + 283.0 + 241.8 = +131.3 kJ
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What is the hybridization of CH3F?

7/23/2020

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The hybridization the carbon atom in CH3F is sp3. We know this because of the tetrahedral arrangement of atoms around the carbon.

The fluorine atom is also sp3 hybridized. The single bond to carbon and the three lone pairs are four "electron groups" which are also tetrahedrally arranged around the F atom - but that is difficult to see from a Lewis structure.
Picture

Edit, in August 2020: I have decided to answer questions like this one on a new site, www.lewis-structure.com. This molecule in particular was made into my first post, which is at http://lewis-structure.com/ch3f-lewis-structure-and-ch3f-hybridization/ 
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Created by Nathan Oldridge (aka ChemistNATE).  All lessons here are Public Domain.