UNIT 3 Flashcards
what happens when reaction rate is low?
if the reaction rate is too low, the reaction may take too long to produce products and may not generate enough profit
what happens when reaction rate is too high?
there is more chance of thermal explosion
what are the two equations for reaction rate and time?
rate = 1/time time = 1/rate
what is collision theory?
collision theory states that for a chemical reaction to be successful the reactant particles must collide and have an energy greater than or equal to the activation energy. They also must have the correct collision geometry.
what happens when you increase the concentration or pressure of the reactant?
it increases the rate of reaction as there are more collisions occurring
how can particle size impact the rate of a reaction?
using powders instead of solid lumps leads to an increase in reaction rate because they have a larger surface area as reactions occur at surfaces so increasing surface area will lead to more collision
what is temperature in terms of reaction rate?
temperature is a measure of the average kinetic energy of all particles in a reaction. it also increases the number of collisions.
what happens as temperature increases in a reaction?
increasing the temperature gives all the particles more energy so more are likely to have energy greater than or equal to the activation energy
what is activation energy?
it is the minimum energy required for colliding particles to form an activated complex
what is collision geometry?
the relative positions of the reactant particles as they collide
what is an activated complex?
an activated complex is an unstable arrangement of atoms of high energy formed at the top of an activation energy curve. it is intermediate between reactants and products.
what are potential energy diagrams used for?
they are used to show the change in energy as a reaction progresses from reactants to products
what are exothermic reactions and how is this illustrated?
they are reactions which give out heat energy due to reactants releasing energy and potential energy diagrams will show that the products have less energy than the reactants.
what are endothermic reactions?
a reaction in which there is a temperature drop in surroundings caused by the reactants taking in energy. a potential energy diagram will show that the products have more energy than the reactants
where is the activated complex?
the activated complex is shown at the top of the activation energy barrier
what is enthalpy change?
enthalpy change is the difference between the product and the reactant. ΔH
how is the effect of the catalyst shown?
it is shown by activation energy being lower than the uncatalysed reaction
what is the enthalpy change in endothermic and exothermic reactions?
endothermic - positive as reactants have lower energy than product
exothermic - negative as reactants have more energy than product
how is the activated complex formed?
reactants –> activated complex –> products
what is a catalyst?
a catalyst alters the rate of a reaction without being used up in the reaction They increase the reaction rate by providing an alternative reaction pathway with a lower activation energy
what is the kinetic energy of particles?
kinetic energy varies from particle to particle but but most have kinetic energy close to the average energy
what is the enthalpy of combustion?
an enthalpy of combustion is the enthalpy change when 1 mole of a substance burns completely
where can you find enthalpies of combustion for certain elements?
the enthalpies of combustion for selected elements and compounds are listed in the SQA data booklet and can be used to relate the mass of a substance to the energy released.
how can enthalpy be calculated?
E=cmΔT
C = specific heat capacity of water M = mass of water being heated ΔT = the difference between the starting temperature and the highest temperature of the water
what is Hess’s law?
states that the enthalpy change for a chemical reaction is independent of the route taken. This allows enthalpy changes to be calculated for reactions that may be difficult to preform experimentally/
how to solve Hess’s law equations?
adding/subtracting/multiplying enthalpies of combustion
what is molar bond enthalpy?
a molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule
what is a mean molar bond enthalpy?
the average energy needed to break one mole of bonds (over a number of compounds with this bond)
how can enthalpy change be calculated for a gas-phase reaction?
they can be calculated by using molar bond enthalpies. this is done by adding the energies needed to break the bonds in the reactants to the total energy released when new product bonds are formed.
what is a closed system?
reaction conditions that prevent reactants and products from leaving the reactant mixture?
how does a dynamic equilibrium occur?
a dynamic equilibrium occurs in a closed system when the rates of the forward and reverse reactions are the same.
what happens when equilibrium is reached?
the concentrations of the reactants/products are constant but will unlikely be equal
what happens when chemists control the rate of reaction?
the reaction conditions shift an equilibrium towards the right
how can concentration affect equilibrium?
when there is an addition of reactant or removal of product = equilibrium shifts to the right/towards the product
when there is an addition of a product or removal of reactant = equilibrium shifts to the left/the reactants
how can temperature affect equilibrium?
increase in temperature - shifts in direction of endothermic reaction
decrease in temperature - shifts in the direction of exothermic reaction
how can pressure affect equilibrium?
increase in pressure = shifts in the direction which reduces the number of molecules in gas phase
decrease in pressure = shifts in the direction which increases the number of molecules in gas phase
how can a catalyst affect equilibrium?
it has no affect on equilibrium position; equilibrium is attained more rapidly
what is chromatography used for?
it is used to separate the components in a mixture
separation depends on the size and polarity of the molecules
what is retention time?
how long it takes for a compound in a mixture to travel along a chromatography column. large molecules have a longer retention time than smaller molecules
what is polarity?
how charged a molecule is
how does a chromatography work?
if a chromatography column is made using polar molecules, a polar compound in a mixture will be strongly attracted to the column and takes longer to move along the column.
what is volumetric analysis?
this involves using a solution of known concentration to determine the unknown concentration of another solution
what does concordant mean?
the results from a titration are within 0.2cm of each other
what is a standard solution?
a solution of accurately known concentration
what does self indicating mean?
a titration in which no indicator is needed because a colour change happens due to the reaction during the titration
what happens to the reaction when the reaction reaches equilibrium?
the reaction does not stop
how can pressure effect equilibrium?
it moves towards the side with the most moles
