1# Rates and Equilibria 2 3## Energy profile diagrams 4 5$$E_A = E_{\text{max}} - E_{\text{initial}}$$ 6 7- Energy always needed to initiate reaction (break bonds of reactants) 8- Reactant particles must collide at correct angle, energy etc 9- Most collisions are not fruitful 10 11 12 13 14**Ways to increase rate of reaction:** 15 161. Increase surface area 172. Increase concentration/pressure 183. Increase temperature 19 20## Kinetic energy 21 22Temperature - measure of _avg_ kinetic energy of particles. Over time each particle will eventually have enough energy to overcome $E_A$. 23Note same distribution indicates same temperature. 24 25 26## Catalysts 27 28- alternate reaction pathway, with lower $E_A$ 29- increased rate of reaction 30- involved in reaction but regenerated at end 31 32**Homogenous** catalyst: same state as reactants and products, e.g. Cl* radicals. 33**Hetrogenous** catalyst: different state, easily separated. Preferred for manufacturing. 34 35 36Many catalysts involve transition elements. 37Haber process (ammonia producition) - enzymes are catalysts for one reaction each. Adsorption (bonding on surface) forms ammonia \ce{NH3} 38 39## Equilibrium systems 40 41**Equilibrium** - the stage at which quantities of reactants and products remain unchanged 42Reaction graphs - exponential/logarithmic curves for reaction rates with time (simultaneous curves forward/back) 43 44## Equilirbium constant $K_C$ 45 46For reaction $aA + bB + cC + dD + \dots \leftrightarrow zZ + yY + xX + \dots$: 47 48$$K_c = {{[Z]^z [Y]^y [X]^x \dots} \over {[A]^a [B]^b [C]^c [D]^d \dots}}$$ 49 50Indicates extent of reaction. If value is high ($> 10^4$), then [products] > [reactants]. If value is low ($< 10^4$), then [reactants] > [products]. 51 52If $K_c$ is small, equilibrium lies *to the left*. 53 54**$K_c$ depends on direction that equation is written (L->R)** 55 56## Reaction constant $Q$ 57 58Same for as $K_C$. If $Q=K_c$, then reaction is at equilibrium. 59 60## Le Châtelier’s principle 61 62> Any change that affects the position of an equilibrium causes that equilibrium to shift, if possible, in such a way as to partially oppose the effect of that change. 63 64### Changing volume 65 661. $\Delta V \implies [\Sigma \text{particles}] \uparrow$, therefore system reacts in direction that produces less particles 672. $\Delta V \implies [\Sigma \text{particles}] \uparrow$, therefore system reacts in direction that produces more particles 682. $n(\text{left}) = n(\text{right})$ (volume change does not disturb equilibrium) 69 70### Changing temperature 71 72Only method that alters $K_c$. 73 74Changing temperature changes kinetic energy. System's response depends on whether reaction is exothermic or endothermic. 75 76- Exothermic - increase in temperature decreases $K_c$ 77- Endothermic - increase in temperature increases $K_c$ 78 79Time-concentration graph: smooth change 80 81## Yield 82 83$$\text{yield %} = {{text{actual mass obtained} \over {theoretical maximum mass}} \times 100$$ 84 85 86