topic 7 - rates of reactions and energy changes Flashcards
what core practical investigates the effect of changing the conditions of a reaction on the rates of reaction?
- measure production of gas between HCl and marble chips
-> size of marble ships changes (smaller chips = larger surface area - faster rate) - observe a colour change in reaction between sodium thiosulfate and HCl (changing conc. - greater number of particles - faster rate) - x dissapears
suggest a practical method which can be used to determine the rate of a given reaction?
- using amount of product used or formed over time
what is the formula for the rates of reaction?
amount of reactant used / time
or
amount of product formed / time
what is units of rate of reaction given as?
g/s or cm3/s
how can you measure the amount of reactant used?
if a gas you can measure volume using a gas syringe
what is the collision theory?
when the reacting particles collide with enough energy
what is the minimum amount of energy required in the collision theory called?
activation energy
what ways increase frequency/energy of collisions?
-increasing temperature
-pressure
-concentration
-surface area
-catalyst
what is the effect of increasing the temperature on the energy of collisions (rate of reaction)?
- increases rate of reaction
- increases kinetic energy so they collide more frequently and energetically
what is the effect of increasing the concentration on the energy of collisions (rate of reaction)?
- increases rate of reaction
- increases number of particles in a given volume and increases frequency of collisions
what is the effect of increasing the surface area on the energy of collisions (rate of reaction)?
- increases rate of reaction
- increases surface available for collisions
- increases frequency of collisions
what is the effect of increasing the pressure on the energy of collisions (rate of reaction)?
- increases rate of reaction
- increases number of particles in given volume
- increases frequency of collisions
how do you interpret graphs of mass, volume or concentration of reactant/products over time?
- draw tangent to curves and use slope to measure rate of reaction
- gradient = rate of reaction
-> steeper line = increase in rate
what is a catalyst?
substances that speed up chemical reactions without altering the products of the reaction, being itself unchanged chemically and in mass at end of reaction
what does adding a catalyst do?
decrease the activation energy - provide alternate pathway and increases proportion of particles with energy
what are enzymes?
biological catalysts
why is yeast an important enzyme?
used in production of ethanol as is fermented from sugars
-> then used in alcoholic drinks
what is the theory of the conservation of energy?
energy is neither created or destroyed
what type of reaction is salt dissolving in water?
either exothermic or endothermic
what type of reaction is neutralisation?
exothermic
what type of reaction is displacement?
exothermic or endothermic
what type of reaction is a precipitation?
exothermic
describe an exothermic reaction
one that transfers energy to the surroundings from the system
- temperature of surroundings increase
give examples of exothermic reactions (4)
combustion, neutralisation, many oxidation reactions, hand warmers
describe an endothermic reaction
one that takes in energy from the surroundings to the system
- temperature of surroundings decrease
give examples of endothermic reactions
decomposition
what type of reaction is breaking bonds and why?
endothermic - energy supplied to break reactant bonds
what type of reaction is making bonds and why?
exothermic - energy released when bonds in products are formed
what is the overall heat energy change for an exothermic reaction?
more heat energy released in making bonds in products that in breaking bonds in reactants
what is the overall heat energy change for an endothermic reaction?
less heat energy is released in forming bonds in products then required in breaking bonds of reactants
what is the calculation for energy change?
energy in - energy out (using polymer drawings)
what does a negative energy change mean?
reaction is exothermic
what does a positive energy change mean?
reaction is endothermic
explain the term activation energy
the minimum amount of energy by colliding particles for a reaction to occur
