Tutoring chemistry, back bonding might come up. Back bonding is a concept from molecular orbitals. In a molecule with a central 3rd-period nonmetal (such as sulfur or phosphorus), double bonding is possible so that the central atom exceeds an octet. …
Tutoring chemistry, the distinction between cell and battery is noted. In electrochemistry, a cell is a single unit of electrical energy production. A cell comprises an anode and cathode, plus the ingredients and the environment needed for the chemical reaction …
The tutor explains which terminal is the anode, which is the cathode, as well as polarity. In terms of electrochemistry, oxidation occurs at the anode; reduction occurs at the cathode. Perhaps less obvious is the answer to the question, “Which …
Electrochemistry: cells and batteries: anode vs cathode Read more »
The tutor defines two terms relating to auto batteries. The reserve capacity (RC) of a car battery is given in minutes. It’s the duration the battery can discharge 25A at ≥ 10.5V. Ampere hours (Ah), on the other hand, is …
Auto batteries: reserve capacity vs Ah (Amp*hrs) Read more »
The tutor tells a quick hint about calculations with logs. Although base e log (ln) is often used, some lab scientists prefer base 10 log (aka, common log or simply “log”). Typically, of course, logx is assumed to be base …
Math, chemistry: conversion of natural logarithm (ln) to log base 10 Read more »
The tutor implicates the Clausius-Clapeyron equation to explain why combustion is more difficult at lower temperatures. To burn, a fuel must evaporate.1 In colder temperatures, fuel has less tendency to evaporate. For two specific temperatures (T1 and T2), the Clausius-Clapeyron …
Physical chemistry: vapor pressure: why a car may be harder to start in the winter Read more »
The tutor converts, for gasoline, the enthalpy of vaporization from Btu/gal to kJ/mol. The density of gasoline is approx. 6.25lb/gal; its heat of vaporization is 900Btu/gal. Its molar mass is approx. 114g/mol. Then the conversion is 900Btu/gal x 1gal/6.25lb x …
Chemistry: conversion of Hvap from Btu/gal to kJ/mol for gasoline Read more »
The tutor suggests a correction to example 11.2 in Chemistry (sixth edition) by Charles E. Mortimer. Example 11.2 (page 275) of said textbook is about the Clausius-Clapeyron equation. At one point, the equation becomes log(0.526/p1) = 0.491 Then, the antilog …
The tutor explains why mortar hardens over time. A single replacement reaction is of the form AB + C → AC + B The setting of mortar happens by such a reaction: Ca(OH)2 + CO2 → CaCO3 + H2O Ca(OH)2 …
Chemistry: solubility, single replacement reaction: why mortar hardens Read more »
The tutor defines equivalent weight in the context of acids and bases. An equivalent weight of an acid is the mass that yields one mole of H+ ions. Similarly, an equivalent weight of a base is the mass that yields …