C8 Rates and equilibrium

C8 Rates and equilibrium

1. C8.1 Rate of reaction

   • rate of reaction tells you how fast the reaction is / reaction rate is very important in the chemical industry / the rate of reaction must be quick and safe
   • How can you find out the rate of reactions?
     • reactions happen at all sorts of different rates. / some are really fast, others really slow / two ways to measure rate of reaction. you can find out how quickly: the reactants are used up as they make products or the products of the reaction are made. / Mean rate of reaction = (quantity of reactant used / time) = (quantity of product formed / time)

2. C8.2 Collision theory and surface area

   • four main factors that affect rate: temperature, surface area, concentration of solutions or pressure of gasses and the presence of a catalyst. / collision theory: particles need to collide with enough energy to react. / activation energy: the minimum amount of energy particles must have to react.
   • Surface area and reaction rate
     • the larger the surface area to volume ratio is the quicker the reaction / the smaller something is the quicker it reacts than a larger variant of itself / powders quickest, large lumps slowest.

3. C8.3 The effect of temperature

   • when temperature is increased the rate of reaction increases also / collision theory explains it: particles collide more often, particles collide with more energy
   • Particles collide more frequently
     • when an object is heated the energy is transferred to its particles / when particles collide more frequently there's more chances for a reaction
   • Particles collide with more energy
     • particles moving around quickly have more energy / this means when you increase temperature a higher proportion of the collisions will result in a reaction / an increased proportion of particles exceeding the activation energy has a greater effect on rate than the increases frequency of collisions

4. C8.4 The effect of concentration or pressure

   • increasing the reactants in a solution increases the rate of reaction because there are more particles of the reactants moving around in the same volume of solution. / increasing the pressure has the same effect as it is increasing the amount in the set volume.

5. C8.5 The effect of catalysts

   • some reactions only happen at high temperatures. / in industry high temperature reactions cost lots of money / a catalyst is used to lower the activation energy (temperature) / different catalysts are needed for different reactions
   • How catalysts work
     • catalysts do not increase the frequency of reactions, or how energetic reactions are. / catalysts provide an alternative pathway to react that requires a lower activation energy / it increases the effectiveness of the reaction
   • Advantages of catalysts in industry
     • catalysts are often expensive precious metals, but they are efficient / it's usually cheaper to get a catalyst than increase temperature for every reaction. / catalysts save money and energy / in turn reduce climate change as they do not require the reaction to have as much energy put in from burning fossil fuels / catalysts are also not used up in a reaction as so can be repeatably used and used.

6. C8.6 Reversible reactions

   • some reactions are reversible and can go backwards. / reactants are on the left, products on the right
   • Examples of reversible reations
     • salts and their crystallisation's are reversible as if water is added to the crystal it dissolves again / ammonium chloride breaks into ammonia and hydrogen chloride when heated, then when it cools it reacts again to form ammonium chloride

7. C8.7 Energy and reversible reactions

   • if a reaction is exothermic in one direction it is endothermic in the other direction. / energy cannot be created or destroyed, so in a reaction the energy has to come from or go somewhere.

8. C8.8 Dynamic equilibrium

   • when a reversible reaction happens in a closed system it reaches dynamic equilibrium / at the beginning the rate of reactants to products is greater than products to reactants, however as more products are made it eventually reaches a point where the amount of reactants to products are equal to the amount of products to reactants

9. C8.9 Altering conditions

   • Pressure and equilibrium
     • if a reversible reaction happens between gasses then altering pressure can affect the equilibrium mixture. / if pressure is increased equilibrium will shift to reduce the pressure / pressure doesn't change equilibrium if there are equal numbers of molecules of products and reactants
   • Temperature and equilibrium
     • by changing temperature you can alter how many reactants or products are made / if the forward reaction is endothermic then increasing temperature increases products / if the forward reaction is exothermic increasing temperature increases the amount of reactants