chem / midyear-lecture.texon commit [chem] lecture notes (a1eeb92)
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  16\fancyhead[LO,LE]{Unit 3 Chemistry Revision Lecture}
  17\fancyhead[CO,CE]{Andrew Lorimer}
  18
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  20
  21\begin{document}
  22
  23  \title{\large Year 12 Chemistry \\ \huge Unit 3 Revision Lecture \\ \large Monash University \\ presented by Peter Skinner}
  24  \author{Andrew Lorimer}
  25  \date{4 July 2019}
  26  \renewcommand{\abstractname}{}
  27  \maketitle
  28
  29  \section{Course structure}
  30  \begin{itemize}
  31    \item \textbf{Unit 3:} 2 SACs, 16\% of study score
  32      \begin{enumerate}
  33        \item Energy production
  34          \begin{itemize}
  35            \item Obtaining energy from fuels
  36            \item Fuel choices
  37            \item Galvanic cells
  38            \item Fuel cells
  39          \end{itemize}
  40        \item Optimising yield
  41          \begin{itemize}
  42            \item Rate of reactions
  43            \item Extent of reactions
  44            \item Production via electrolysis
  45            \item Rechargable batteries
  46          \end{itemize}
  47      \end{enumerate}
  48    \item \textbf{Unit 4:} 3 SACs, 24\% of study score
  49    \item \textbf{Exam:} 60\% of study score
  50      \begin{itemize}
  51        \item 15 minutes reading time, 2.5 hours writing time
  52        \item 30 multiple choice questions (spend 30---45 minutes, \textbf{do last}) - harder in new study design
  53        \item 90 marks written questions (spend 1 hr 45 m---2 hr)\\
  54          Last year:
  55          \begin{itemize}
  56            \item 23\% calculations (21 marks)
  57            \item 44\% extended answer (40 marks)
  58            \item 32\% short answer (29 marks)
  59          \end{itemize}
  60        \item 5---10 marks on writing chemical equations
  61        \item Same marking panel as last year
  62        \item Indirect assessment of pracs
  63        \item $\ge$ 1 mark for significant figures
  64        \item Importance of written communication
  65        \item First parts are important, no consequential marks
  66        \item Use dot points (short form) - especially in rates \& concentration
  67      \end{itemize}
  68  \end{itemize}
  69  
  70  \begin{tcolorbox}[title=Key points]
  71  \begin{itemize}
  72    \item Spend 30---45 minutes on multiple choice
  73    \item Focus on redox reactions
  74    \item Use data book
  75    \item Multiple choice questions are hard
  76    \item Memorise oxidation numbers
  77  \end{itemize}
  78  \end{tcolorbox}
  79
  80  \section{Energy production}
  81  
  82  \begin{itemize}
  83    \item $C=n \div v$ or $C=m \div V$ (concentration in g L$^{-1}$)
  84    \item Gases: $PV=nRT$ and \colorbox{important}{$n=V \div V_m$}
  85    \item Past exams before 2017 use different SLC
  86    \item Renewability - \textit{reasonable} timeframe
  87    \item Fuel choices - consider:
  88      \begin{itemize}
  89        \item External temperature
  90        \item Viscosity \colorbox{important}{(intermolecular forces)}
  91        \item Hygroscopic properties \colorbox{important}{(attracts water $\implies$ forms H-bonds)}
  92        \item \colorbox{important}{Cloud point}
  93      \end{itemize}
  94    \item Blended fuels - \colorbox{important}{use energy per mass not energy per mol}
  95  \end{itemize}
  96
  97
  98  \section{Yield \& rate}
  99
 100  \begin{itemize}
 101    \item \colorbox{important}{Equilibrium constant $K_C$ needs units}
 102    \item $K_C \equiv K$
 103    \item Example question for rates: limiting factor for rate, given a set (equal) rate of both reactants consumption/production
 104    \item Collision theory:
 105      \begin{enumerate}
 106        \item Particles must collide
 107        \item Particles must collide with sufficient energy to overcome $E_A$
 108      \end{enumerate}
 109    \item Increase of rate with temperature:
 110      \begin{enumerate}
 111        \item $\uparrow$ temperature $\implies \uparrow$ energy $\implies$ more frequent collisions
 112        \item $\uparrow$ temperature $\implies \uparrow$ energy $\implies$ collisions occur with greater energy\\
 113          ($\implies$ greater \textit{proportion} of particles that can react per unit time)
 114      \end{enumerate}
 115    \item $\uparrow c(\text{reactants}) \implies $ more collisions 
 116    \item Definition of \textit{rate}: more products per unit time $\longrightarrow$ faster rate
 117    \item Cause and effect: propose hypothesis and prove by induction
 118    \item Maxwell-Boltzmann distributions - $x_{\text{peak}}$ is constant for different concentrations
 119    \item \colorbox{important}{Memorise definition of \textit{catalyst}:} provides a reaction with an alternative energy pathway which has a lower activation energy
 120  \end{itemize}
 121
 122  \subsection{Equilibria}
 123  \begin{itemize}
 124    \item \colorbox{important}{all} reactants and products are present at equilibrium
 125    \item $K_C$ is fixed at a constant temperature and reaction
 126    \item $K_C$ changes with concentrations (relative)
 127    \item If reaction equation is reversed, $K_C$ value will be the reciprocal
 128    \item If temperature changes, $K_C$ will change (but \colorbox{important}{not necessarily proportionally})
 129    \item Le Chatelier's principle:\\
 130      \textit{If a change is made to a system at equilibrium, \\the system will partially oppose this change \colorbox{important}{if it is possible}}
 131    \item Accuracy of graph drawing - \colorbox{important}{use \textbf{clear} plastic ruler}
 132    \begin{itemize}\item Label vertical ratios\end{itemize}
 133        \item Use concentration table format for calculating equilibrium constant $K_C$
 134  \end{itemize}
 135
 136  \begin{tcolorbox}[title=Important, colback=BurntOrange]
 137    \centering
 138    $K_C$ is \textbf{not} related to the rate of reaction\\
 139    $\implies$ we cannot say how fast a reaction os going to occur from the $K_C$ value
 140  \end{tcolorbox}
 141
 142  \subsection{Exothermic \& endothermic reactions}
 143
 144  \begin{itemize}
 145    \item All combustion reactions are exothermic
 146    \item Data book: molar heat of combustion $= |\Delta H|$
 147    \item Endothermic reactions rarely occur naturally (creates instability/entropy)
 148    \item $E_A=|E_{\text{max}}-E_{\text{initial}}|$
 149    \item \colorbox{important}{If coefficients of a thermochemical equation are changed, $\Delta H$ also changes}
 150    \item Possible data discrepencies in theoretical results:
 151      \begin{itemize}
 152        \item State of \ce{H2O}
 153        \item Incomplete combustion
 154        \item Heat loss to environment
 155      \end{itemize}
 156    \item \colorbox{important}{Analogy with simultaneous equations}
 157    \item Calorimetry - \colorbox{important}{insulate \textit{sides} of can not bottom.} Be specific.
 158  \end{itemize}
 159  Multiple choice question examples (features of \textbf{exothermic} reactions):
 160  \begin{enumerate}[label={\alph*)}]
 161    \item Products are \rule{4em}{0.5pt} as they have less chemical energy than reactants \hfill \textit{(more stable)}
 162    \item \rule{5em}{0.5pt} required to break bonds in products compared to reactants \hfill \textit{(more chemical energy)}
 163  \end{enumerate}
 164  Multiple choice question examples (features of \textbf{endothermic} reactions):
 165  \begin{enumerate}[label={\alph*)}]
 166    \item Transformation of \rule{4em}{0.5pt} energy from surroundings into \rule{4em}{0.5pt} \hfill \textit{(thermal, chemical)}
 167    \item $\therefore$ Surroundings and reaction becomes \rule{4em}{0.5pt} \hfill \textit{(colder)}
 168  \end{enumerate}
 169
 170  \section{Oxidation numbers (memorise)}
 171
 172  \renewcommand{\arraystretch}{1.4}
 173  \begin{tabularx}{0.8\textwidth}{r|X}
 174    \textbf{Species} & \textbf{Rule} \\
 175    \hline
 176    Elements & Always 0 \\
 177    Ions & Same as common ion \\
 178    Hydrogen & +1 (unless present as \ce{H2O} - O.N. = 0; or as hydride - O.N. = -1) \\
 179    Oxygen & -2 (unless present as \ce{O2} - O.N. = 0; or as peroxide - O.N. = -1) \\ 
 180    Molecules & Sum of O.N. must equal zero \\
 181    Molecular ions & Sum of O.N. must equal overall charge on ion
 182  \end{tabularx}
 183
 184  \section{Redox reactions}
 185  \begin{itemize}
 186    \item Verify  equations: check charge of each side independently: charge(LHS) $=$ charge(RHS)
 187    \item Electrochemical series always has \colorbox{important}{oxidants} on left
 188    \item Top left and bottom right always react spontaneously
 189    \item For electrochemical cell questions: first parts are important, no consequential marks
 190    \item Non-standard conditions can alter positions of half-equations on electrochemical series and change $E^0$ values
 191    \item Secondary cells - polarity is constant, but reaction at each electrode swaps
 192  \end{itemize}
 193
 194  \subsection{Galvanic cells}
 195  \begin{itemize}
 196    \item Value of $E^0$ is \textit{not} a reliable indicator for rate of reaction
 197    \item Half cells are physically separate
 198    \item \colorbox{important}{Products must remain in contact with electrodes}
 199  \end{itemize}
 200
 201  \subsection{Electrolytic cells}
 202  \begin{itemize}
 203    \item Possible question: name observations
 204      \begin{itemize}
 205        \item Bubbles
 206        \item \ce{O2} would \textit{not} be visible
 207        \item Cannot \textit{see} $\uparrow [$\ce{H+}$]$
 208        \item Can see \ce{Cu(s)} deposit on electrode
 209        \item Can see colour change (pH) - \ce{Cu2+} solution can be an indicator
 210      \end{itemize}
 211    \item Less side reactions in e.g. lithium ion cells (efficiency)
 212    \item Lower reactions in electrochemical series do not occur forwards (L$\rightarrow$R)
 213    \item Check state of \ce{H2O} - can it be liquid at that temperature?
 214  \end{itemize}
 215
 216  \subsection{Fuel cells}
 217  \begin{itemize}
 218    \item Galvanic cells are primary cells, fuel cells are not primary \colorbox{important}{are they secondary?}
 219    \item Major disadvantage of fuel cells: expensive electrodes (they must also function as catalysts)
 220    \item Fuel cells - same overall reaction as combustion
 221    \item Reactangs must not come into contact
 222    \item Highly efficient
 223  \end{itemize}
 224
 225  \subsection{Electrochemical series}
 226  
 227  \begin{tcolorbox}[colback=SkyBlue]
 228    \centering
 229    Strongest oxidant will always react preferentially with best reductant\\
 230    Always identify \textit{all} chemicals present in reaction on electrochemical series
 231  \end{tcolorbox}
 232
 233\end{document}