# Tutor profile: Peter D.

## Questions

### Subject: Chemistry

Describe the 3 main intermolecular forces between molecules.

The 3 main intermolecular forces between molecules are van der waals (also called dispersion or London dispersion), dipole-dipole (also called polar), and hydrogen bonding. Most every uncharged molecule exhibits van der waals interactions, which are essentially a weak electrostatic attraction between two electron dense molecules. The higher the electron density and the closer the two molecules, the more significant the induced dipole and consequently the more significant the attractive force. Dipole-dipole interactions occur between molecules that have a strong dipole in their structure. For example, let's look at an HCl molecule. It consists of a Hydrogen atom: H, and a Chlorine atom: Cl, bonded by a covalent bond, meaning they are sharing 2 electrons between them. However, in chemistry there is a property of each individual element known as electronegativity, which is the ability of an atom of that element to attract electrons. Because Chlorine has so many more protons in its nucleus, its effective nuclear charge is much higher so it pulls more on the electrons. Because it pulls so much harder on the electrons, more of the negative charge of the electrons is closer to the Cl atom and less is near the H atom, creating a dipole where the H is partially positive and the Cl is partially negative. If two HCl molecules were next to each other, they could re-orient so the partially positive H of one HCl molecule is attracted to the partially negative Cl of the other. This attraction is known as a dipole-dipole interaction/force. Hydrogen bonding is very similar to dipole-dipole interactions but is specific for molecules that have hydrogen bonded to the most electronegative atoms, namely Nitrogen (N), Oxygen (O), and Fluorine (F).

### Subject: Chemical Engineering

What are the assumptions made when conducting a McCabe-Thiele Analysis for a distillation column?

1. Steady-State conditions 2. Binary Mixture 3. Constant Molar Overflow, requiring that: -Negligible heat of mixing -Constant heat of vaporization -Adiabatic trays

### Subject: Algebra

If (x+1)/((y+5)^2)=y^5 Find an expression for x in terms of y

For a question like this, the goal is to isolate x by itself. Generally speaking when approaching a problem like this, simplifying complex fractions by multiplying both sides of the equation by the denominator is probably the best approach. In this case, multiplying both sides by (y+5)^2, the equation simplifies to x+1=y^5*((y+5)^2). Now we can foil the (y+5)^2 term, which becomes y^2+10y+25, then multiply through by the y^5 term to get this equation: x+1=y^7+10y^6+25y^5. Remember that when multiplying by an exponent you add the exponents together, hence why the y^2*y^5 becomes y^7 for example. Now to isolate x, we can just subtract 1 from both sides, and the final expression is x=y^7+10y^6+25y^5-1.

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