From: Andrew Lorimer Date: Fri, 12 Jul 2019 07:47:20 +0000 (+1000) Subject: [chem] lecture notes X-Git-Tag: yr12~94 X-Git-Url: https://git.lorimer.id.au/notes.git/diff_plain/a1eeb92f082ac3563ac5a31fe1ffa0d078174cc9 [chem] lecture notes --- diff --git a/chem/midyear-lecture.pdf b/chem/midyear-lecture.pdf new file mode 100644 index 0000000..faff32c Binary files /dev/null and b/chem/midyear-lecture.pdf differ diff --git a/chem/midyear-lecture.tex b/chem/midyear-lecture.tex new file mode 100644 index 0000000..f3b45a1 --- /dev/null +++ b/chem/midyear-lecture.tex @@ -0,0 +1,233 @@ +\documentclass[a4paper]{article} +\usepackage[dvipsnames]{xcolor} +\usepackage[a4paper,margin=2cm]{geometry} +\usepackage{multicol} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{enumitem} +\usepackage{tcolorbox} +\usepackage{fancyhdr} +\usepackage{pgfplots} +\usepackage{tabularx} +\usepackage{mhchem} +\definecolor{important}{HTML}{ff9933} + +\pagestyle{fancy} +\fancyhead[LO,LE]{Unit 3 Chemistry Revision Lecture} +\fancyhead[CO,CE]{Andrew Lorimer} + +\setlength\parindent{0pt} + +\begin{document} + + \title{\large Year 12 Chemistry \\ \huge Unit 3 Revision Lecture \\ \large Monash University \\ presented by Peter Skinner} + \author{Andrew Lorimer} + \date{4 July 2019} + \renewcommand{\abstractname}{} + \maketitle + + \section{Course structure} + \begin{itemize} + \item \textbf{Unit 3:} 2 SACs, 16\% of study score + \begin{enumerate} + \item Energy production + \begin{itemize} + \item Obtaining energy from fuels + \item Fuel choices + \item Galvanic cells + \item Fuel cells + \end{itemize} + \item Optimising yield + \begin{itemize} + \item Rate of reactions + \item Extent of reactions + \item Production via electrolysis + \item Rechargable batteries + \end{itemize} + \end{enumerate} + \item \textbf{Unit 4:} 3 SACs, 24\% of study score + \item \textbf{Exam:} 60\% of study score + \begin{itemize} + \item 15 minutes reading time, 2.5 hours writing time + \item 30 multiple choice questions (spend 30---45 minutes, \textbf{do last}) - harder in new study design + \item 90 marks written questions (spend 1 hr 45 m---2 hr)\\ + Last year: + \begin{itemize} + \item 23\% calculations (21 marks) + \item 44\% extended answer (40 marks) + \item 32\% short answer (29 marks) + \end{itemize} + \item 5---10 marks on writing chemical equations + \item Same marking panel as last year + \item Indirect assessment of pracs + \item $\ge$ 1 mark for significant figures + \item Importance of written communication + \item First parts are important, no consequential marks + \item Use dot points (short form) - especially in rates \& concentration + \end{itemize} + \end{itemize} + + \begin{tcolorbox}[title=Key points] + \begin{itemize} + \item Spend 30---45 minutes on multiple choice + \item Focus on redox reactions + \item Use data book + \item Multiple choice questions are hard + \item Memorise oxidation numbers + \end{itemize} + \end{tcolorbox} + + \section{Energy production} + + \begin{itemize} + \item $C=n \div v$ or $C=m \div V$ (concentration in g L$^{-1}$) + \item Gases: $PV=nRT$ and \colorbox{important}{$n=V \div V_m$} + \item Past exams before 2017 use different SLC + \item Renewability - \textit{reasonable} timeframe + \item Fuel choices - consider: + \begin{itemize} + \item External temperature + \item Viscosity \colorbox{important}{(intermolecular forces)} + \item Hygroscopic properties \colorbox{important}{(attracts water $\implies$ forms H-bonds)} + \item \colorbox{important}{Cloud point} + \end{itemize} + \item Blended fuels - \colorbox{important}{use energy per mass not energy per mol} + \end{itemize} + + + \section{Yield \& rate} + + \begin{itemize} + \item \colorbox{important}{Equilibrium constant $K_C$ needs units} + \item $K_C \equiv K$ + \item Example question for rates: limiting factor for rate, given a set (equal) rate of both reactants consumption/production + \item Collision theory: + \begin{enumerate} + \item Particles must collide + \item Particles must collide with sufficient energy to overcome $E_A$ + \end{enumerate} + \item Increase of rate with temperature: + \begin{enumerate} + \item $\uparrow$ temperature $\implies \uparrow$ energy $\implies$ more frequent collisions + \item $\uparrow$ temperature $\implies \uparrow$ energy $\implies$ collisions occur with greater energy\\ + ($\implies$ greater \textit{proportion} of particles that can react per unit time) + \end{enumerate} + \item $\uparrow c(\text{reactants}) \implies $ more collisions + \item Definition of \textit{rate}: more products per unit time $\longrightarrow$ faster rate + \item Cause and effect: propose hypothesis and prove by induction + \item Maxwell-Boltzmann distributions - $x_{\text{peak}}$ is constant for different concentrations + \item \colorbox{important}{Memorise definition of \textit{catalyst}:} provides a reaction with an alternative energy pathway which has a lower activation energy + \end{itemize} + + \subsection{Equilibria} + \begin{itemize} + \item \colorbox{important}{all} reactants and products are present at equilibrium + \item $K_C$ is fixed at a constant temperature and reaction + \item $K_C$ changes with concentrations (relative) + \item If reaction equation is reversed, $K_C$ value will be the reciprocal + \item If temperature changes, $K_C$ will change (but \colorbox{important}{not necessarily proportionally}) + \item Le Chatelier's principle:\\ + \textit{If a change is made to a system at equilibrium, \\the system will partially oppose this change \colorbox{important}{if it is possible}} + \item Accuracy of graph drawing - \colorbox{important}{use \textbf{clear} plastic ruler} + \begin{itemize}\item Label vertical ratios\end{itemize} + \item Use concentration table format for calculating equilibrium constant $K_C$ + \end{itemize} + + \begin{tcolorbox}[title=Important, colback=BurntOrange] + \centering + $K_C$ is \textbf{not} related to the rate of reaction\\ + $\implies$ we cannot say how fast a reaction os going to occur from the $K_C$ value + \end{tcolorbox} + + \subsection{Exothermic \& endothermic reactions} + + \begin{itemize} + \item All combustion reactions are exothermic + \item Data book: molar heat of combustion $= |\Delta H|$ + \item Endothermic reactions rarely occur naturally (creates instability/entropy) + \item $E_A=|E_{\text{max}}-E_{\text{initial}}|$ + \item \colorbox{important}{If coefficients of a thermochemical equation are changed, $\Delta H$ also changes} + \item Possible data discrepencies in theoretical results: + \begin{itemize} + \item State of \ce{H2O} + \item Incomplete combustion + \item Heat loss to environment + \end{itemize} + \item \colorbox{important}{Analogy with simultaneous equations} + \item Calorimetry - \colorbox{important}{insulate \textit{sides} of can not bottom.} Be specific. + \end{itemize} + Multiple choice question examples (features of \textbf{exothermic} reactions): + \begin{enumerate}[label={\alph*)}] + \item Products are \rule{4em}{0.5pt} as they have less chemical energy than reactants \hfill \textit{(more stable)} + \item \rule{5em}{0.5pt} required to break bonds in products compared to reactants \hfill \textit{(more chemical energy)} + \end{enumerate} + Multiple choice question examples (features of \textbf{endothermic} reactions): + \begin{enumerate}[label={\alph*)}] + \item Transformation of \rule{4em}{0.5pt} energy from surroundings into \rule{4em}{0.5pt} \hfill \textit{(thermal, chemical)} + \item $\therefore$ Surroundings and reaction becomes \rule{4em}{0.5pt} \hfill \textit{(colder)} + \end{enumerate} + + \section{Oxidation numbers (memorise)} + + \renewcommand{\arraystretch}{1.4} + \begin{tabularx}{0.8\textwidth}{r|X} + \textbf{Species} & \textbf{Rule} \\ + \hline + Elements & Always 0 \\ + Ions & Same as common ion \\ + Hydrogen & +1 (unless present as \ce{H2O} - O.N. = 0; or as hydride - O.N. = -1) \\ + Oxygen & -2 (unless present as \ce{O2} - O.N. = 0; or as peroxide - O.N. = -1) \\ + Molecules & Sum of O.N. must equal zero \\ + Molecular ions & Sum of O.N. must equal overall charge on ion + \end{tabularx} + + \section{Redox reactions} + \begin{itemize} + \item Verify equations: check charge of each side independently: charge(LHS) $=$ charge(RHS) + \item Electrochemical series always has \colorbox{important}{oxidants} on left + \item Top left and bottom right always react spontaneously + \item For electrochemical cell questions: first parts are important, no consequential marks + \item Non-standard conditions can alter positions of half-equations on electrochemical series and change $E^0$ values + \item Secondary cells - polarity is constant, but reaction at each electrode swaps + \end{itemize} + + \subsection{Galvanic cells} + \begin{itemize} + \item Value of $E^0$ is \textit{not} a reliable indicator for rate of reaction + \item Half cells are physically separate + \item \colorbox{important}{Products must remain in contact with electrodes} + \end{itemize} + + \subsection{Electrolytic cells} + \begin{itemize} + \item Possible question: name observations + \begin{itemize} + \item Bubbles + \item \ce{O2} would \textit{not} be visible + \item Cannot \textit{see} $\uparrow [$\ce{H+}$]$ + \item Can see \ce{Cu(s)} deposit on electrode + \item Can see colour change (pH) - \ce{Cu2+} solution can be an indicator + \end{itemize} + \item Less side reactions in e.g. lithium ion cells (efficiency) + \item Lower reactions in electrochemical series do not occur forwards (L$\rightarrow$R) + \item Check state of \ce{H2O} - can it be liquid at that temperature? + \end{itemize} + + \subsection{Fuel cells} + \begin{itemize} + \item Galvanic cells are primary cells, fuel cells are not primary \colorbox{important}{are they secondary?} + \item Major disadvantage of fuel cells: expensive electrodes (they must also function as catalysts) + \item Fuel cells - same overall reaction as combustion + \item Reactangs must not come into contact + \item Highly efficient + \end{itemize} + + \subsection{Electrochemical series} + + \begin{tcolorbox}[colback=SkyBlue] + \centering + Strongest oxidant will always react preferentially with best reductant\\ + Always identify \textit{all} chemicals present in reaction on electrochemical series + \end{tcolorbox} + +\end{document}