Chemical kinetics

• chemical kinetics (or reaction kinetics)
• collision theory
• reaction mechanism

Reaction rate

• reaction rate (or rate of reaction) (קצב תגובה, מהירות תגובה)

  • For $a\mathrm{A}+b\mathrm{B}\to p\mathrm{P}+q\mathrm{Q}$
    • $a,b,p,q$ are the stoichiometric coefficients
    • $v=-\frac{1}{a}\frac{d[\mathrm{A}]}{dt}=-\frac{1}{b}\frac{d[\mathrm{B}]}{dt}=\frac{1}{p}\frac{d[\mathrm{P}]}{dt}=\frac{1}{q}\frac{d[\mathrm{Q}]}{dt}$
  • symbols: $v$, $\nu$, $r$, $R$, $\text{Rate}$
  • units: $\text{M/s}$ (molarity per second)

• rate equation (or rate law or empirical differential rate equation)

• reaction rate constant (or rate coefficient) $k$

  • Arrhenius equation

$a\mathrm{A}\to \mathrm{products}$

• $v=k[\mathrm{A}{]}^n$, where:
  • $n$ is the reaction order (determined experimentally. It is not necessarily $n=a$ unless the reaction is elementary)

	zero-order ($n=0$)	first-order ($n=1$)	second-order ($n=2$)
differential rate law	$\text{Rate}=k$	$\text{Rate}=k[\text{A}]$	$\text{Rate}=k[\text{A}{]}^2$
integrated rate law	$[\text{A}{]}_t=-kt+[\text{A}{]}_0$	$\ln [\text{A}{]}_t=-kt+\ln [\text{A}{]}_0$	$\frac{1}{[\text{A}{]}_t}=kt+\frac{1}{[\text{A}{]}_0}$
alternative integrated form	$[\text{A}{]}_0-[\text{A}{]}_t=kt$	$[\text{A}{]}_t=[\text{A}{]}_0{e}^{-kt}$	$\frac{[\text{A}{]}_0-[\text{A}{]}_t}{[\text{A}{]}_0[\text{A}{]}_t}=kt$
unit of $k$	$\text{M}\cdot {\text{s}}^{-1}$	${\text{s}}^{-1}$	${\text{M}}^{-1}\cdot {\text{s}}^{-1}$
half-life ($t_{1/2}$)	$t_{1/2}=\frac{[\text{A}{]}_0}{2k}$	$t_{1/2}=\frac{\ln (2)}{k}\approx \frac{0.693}{k}$	$t_{1/2}=\frac{1}{k[\text{A}{]}_0}$

$a\mathrm{A}+b\mathrm{B}\to \mathrm{products}$

• $v=k[\mathrm{A}{]}^m[\mathrm{B}{]}^n$ where:
  • $n$ and $m$ are the partial orders, and $m+n$ is the overall order
    • determined experimentally. It is not necessarily $n=b,m=a$ unless the reaction is elementary

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• activated complex (קומפלקס משופעל, תצמיד משופעל)

  • transition state (מצב מעבר)

• activation energy ($E_a$) (אנרגיית שפעול)

• effective collision (התנגשות פוריה)

• catalysis (זֵירוז, קִטלוז, קטליזה)

  • catalyst (זָרָז, קָטָלִיזָטוֹר)

Chemical equilibrium

• chemical equilibrium (שיווי משקל כימי)

  • cf. dynamic equilibrium

• equilibrium reaction

  • ”When the reactants in a chemical reaction are initially in a Boltzmann distribution the reaction is referred to as an equilibrium reaction.” (IUPAC)

• homogeneous equilibrium (all reactants and products are in the same physical phase)

• heterogeneous equilibrium

• equilibrium constant ($K_{\text{eq}}$) (קבוע שיווי-משקל) (of a substance in a given temperature)

  • dimensionless
  • equilibrium-constant expression
    • terms of concentration:
      • $K_c=\frac{[\mathrm{C}{]}^c[\mathrm{D}{]}^d}{[\mathrm{A}{]}^a[\mathrm{B}{]}^b}$
    • terms of partial pressure:
      • $K_p=\frac{(P_{\mathrm{C}}{)}^c(P_{\mathrm{D}}{)}^d}{(P_{\mathrm{A}}{)}^a(P_{\mathrm{B}}{)}^b}$
    • $K_p=K_c(RT{)}^{\Delta n}$
  • (see also dissociation constant)

• todo

  • In equilibrium expressions, pure solids and liquids are omitted because their activities are unity in their standard states. In rate law, their concentrations are not variable and are incorporated into $k$; however, the rate can depend on factors such as surface area in heterogeneous systems.

• law of mass action (חוק פעולת המסות)

• equilibrium position

• reaction quotient ($Q$)

• reversible process (תהליך הפיך)

  • irreversible process (תהליך בלתי הפיך)
  • $\rightleftharpoons$

• reversible reaction

  • $a\mathrm{A}+b\mathrm{B}\rightleftharpoons c\mathrm{C}+d\mathrm{D}$
  • forward reaction
  • reverse reaction

• Le Chatelier’s principle

  • ”If a system at equilibrium is disturbed by a change in temperature, pressure, or a component concentration, the system will shift its equilibrium position so as to counteract the effect of the disturbance” (Brown, 2012)

References

• Brown, Theodore L. (2012). Chemistry. Prentice Hall.