c8 - rates and equilibrium Flashcards
define rate of reaction
speed of a reaction
how can you work out rate of a chemical reaction?
- find out how quickly reactants are used up as they make products
- find out how quickly the products of the reaction are made
how can you find out how quickly reactants are used up in some reactions?
by measuring the mass of the reactant mixture
- if reaction gives off a gas, then mass of mixture decreases
how can gradient of a graph help us work out rate of reaction?
the steeper the gradient, the faster the reaction is at that time
how can a graph for rate of reaction be produced?
by measuring the mass of gas released or volume of gas produced at intervals of time
give the two possible equations for mean rate of reaction after a given time.
mean rate of reaction = quantity of reactant used/ time taken OR quantity of product formed/ time taken
define collision theory
states that reactions only happen if particles collide
define activation energy
minimum energy particles need to react
give two ways of increasing rate of reaction
1) increasing frequency of reacting particles colliding with eachother
2) increase the energy they have when they collide
what happens when you increase frequency of collisions or energy of particles?
rate of reaction will increase
give factors for increasing rate of reaction
- increasing temperature
- increase concentration of reactants in solids
- increase pressure of reacting gases
- increase surface area of solids
how can rate of reaction be increased through surface area?
1) breaking large solids into smaller pieces exposes more surface area
2) this leads to more collisions and so a powder reacts faster than large lumps
3) finer the powder, faster the reaction
why do powders react faster than large pieces of solid?
more surface area
what happens to rate of reaction when temperatures increase?
increases
- because particles collide more often
- particles collide with more energy
what happens to particles when there is a rise of 10 degrees from room temperature/
rate of reactions is doubled, so particles collide twice as fast
what must you remember when talking about particles in an exam?
don’t say ‘more collisions’ instead say ‘more frequent collisions’ or ‘collisions occur more often’
what happens to rate of reaction when you increase the concentration?
- increases rate of reaction because there are more particles of the reactants moving around in the same volume of solution.
- increased frequency of collisions results in a faster reaction
what happens to rate of reactions when pressure is increased?
- increased pressure squashes gas particles more closely together
- more particles of a gas in a given space
- produces more frequent collisions so increases rate of reaction
how can you find rate of reaction?
- by plotting volume of gas given off as reaction progresses over time
- see how long it takes to collect a fixed volume of gas using same apparatus
define a catalyst
- changes rate of reaction
- not used up or changed chemically in reaction so can be reused
how do catalysts increase rate of reaction?
- provide an alternative reaction pathway to the products with a lower activation energy
- higher proportion of the reactant particles have sufficient energy to react
- frequency of effective collisions increases
what benefits does using catalysts in industrial processes have?
- they can reduce energy and time needed for reactions
- this reduces cost and reduces impact on environment
define reversible reactions
when products react together to make original reactants again
how are reversible reactions presented?
2 ‘half arrows’ are used
- one point forward, one points backwards
what happens when ammonium chloride is heated?
decomposes to produce ammonia gas and hydrogen chloride gas
what happens when ammonia gas and hydrogen chloride gas cool down?
they react to form ammonium chloride again
in reversible reactions, the forwards and reverse reactions involve…
equal but opposite energy tranfers
amount of energy released by the exothermic reaction…
exactly equals the amount taken in by the endothermic reaction
if a reversibe reaction is exothermic in one directions…
must be endothermic in the other
what happens when you heat blue hydrated copper (II) sulfate crystals
an endothermic reaction (exothermic reverse)
what happens when water is added to anhydrous copper (II) sulfate?
hydrated copper (II) sulfate is formed
- exothermic reaction in this direction
define anhydrous
substance that doesn’t contain water
why must blue copper (II) sulfate be heated continuously to change it into anhydrous copper (II) sulfate?
the water is driven off, producing anhydrous copper sulfate which is a white solid
- endothermic reaction
what does blue hydrated copper (II) mean?
copper and sulfate ions in its crystal structure are surrounded by water molecules
why does adding water to anhydrous copper (II) sulfate cause mixture to get hot?
- Hydrogen bonding occurs between the solute and the solvent, releasing energy
- exothermic reactions
define closed system
no reactants or products can escape
what happens in a reversible reaction when rate of forward reaction equals rate of backwards reaction?
equilibrium is reached
define equilibrium
both reactions continue to happen, but amount of reactants and products remain constant
how can you change relative amounts of reactants and products in a reacting mixture at equlibrium?
change conditions
- this is important for chemical industry in controlling reactions
define le chatelier’s principle
when a change in conditions is introduced to a system at equilibrium, the positiion of equilibrium shifts as to cancel out the change
what happens if you increase concentration of a reaction
will cause more products to be formed as system tries to achieve equilibrium
what happens if you remove a product?
more reactants will try and achieve equilibrium so more product is formed
what happens if the forward reaction produces more molecules of gas?
- an increase in pressure decreases amount of products formed
- decrease in pressure increases amount of products formed
what happens if forward reaction produces fewer molecules of gas?
- an increase in pressure increases amount of products formed
- decrease in pressure decreases amount of products formed
what happens if forward reaction is exothermic?
- increase in temperature decreases amount of products formed
- decrease in temperature increases amount of products formed
what happens if forward reaction is endothermic?
- increase in temperature increases amount of products formed
- decrease in temperature decreases amount of products formed
why would rate decrease during a reaction?
- particles being used up
- less chance of collision
