chemistry

Statistical Treatment of Analytical Data - One-Sample t-test Home > Statistics – Frequency Distributions, Normal Distribution, z-scores > Statistics – Frequency Distributions, Normal Distribution, z-scores Statistical Treatment of Analytical Data - One-Sample t-test in Chemical Analysis A one-sample t-test is used to compare two means provided that data are normally distributed (plot of the frequencies of data is a histogram of normal distribution ). A t-test is a parametric test and relies on distributional assumptions. It is a useful tool in analytical work when two means have to be compared. A situation like this is presented in the following example. A new analytical instrument is tested in a chemical laboratory by determining the mass m (in mg) of Cu contained in a certain mass (i.e. 1 g) of a certified reference material (CRM). The analysis certificate of the CRM states that the average mass of Cu (in mg) is 4.54 per

Solved Examples - Entropy changes and thermodynamic equilibrium Entropy Changes ΔS and Thermodynamic Equilibrium – Solved Examples   In a previous post entitled “ Entropy, Free Energy and Thermodynamic Equilibrium ” the Boltzmann definition of entropy was given and how entropy changes ΔS are associated with chemical processes was discussed. Below, some examples are given regarding entropy changes ΔS and chemical reactions. Example #1 Choose the reaction expected to have the greatest increase in entropy: a)  N 2 (g) + O 2 (g) ———› 2 NO(g) b)  H 2 O (l)    ———›   H 2 O (g) c)  2 XeO 3 (s)  ———›   2 Xe(g) + 3 O 2 (g) d) C(s) + O 2 (g)   ———›  CO 2 (g)   Answer: The reaction with the greatest increase in the moles of gas will have the greatest increase in entropy . Answer (c) is correct. In general, when a reaction involves gaseous molecules and the number of gaseous products (or moles of gaseous products) is greater than the number of molecules

Entropy, free energy and thermodynamic equilibrium Entropy, Free Energy and Thermodynamic Equilibrium Chemical reactions are performed by mixing the reactants and regulating external conditions such as temperature and pressure . Two basic questions though arise: Is it possible for the reaction to occur at the selected conditions? If the reaction proceeds, what determines the ratio of products and reactants at equilibrium?   Both questions are answered by chemical thermodynamics : Thermodynamics can tell us whether a proposed reaction is spontaneous (possible) under particular conditions even before the actual experiment. Thermodynamics can also predict the ratio of products and reactants at equilibrium provided that the reaction is spontaneous . Note: Thermodynamics cannot answer though how fast a reaction will proceed. The field of Chemical Kinetics studies reaction rates. After many years of observation scientists concluded th