Part of physical chemistry – IGCSE chemistry – Flashcards

A compound formed when hydrogen ion of an acid is replaced by a metal ion or An Ammonium ion

An insoluble solid formed during a reaction of water soluble reactants - identified by the appearance of cloudiness in the container

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In an exothermic reaction heat is given out. Because bonds are made which gives out energy. Think expelled; exit; exo. In a endothermic reaction heat is taken in. Because bonds are Broken which requires energy.

Measure the temperature at the beginning of the experiment, measure the temperature at the end. How ever much heat has gone up or down is the calorimetry of the reaction. For example if you have a beaker of water and take its temperature, then burn a piece of bread under it, the change in temperature is the calories (energy) of the bread.

?H is the symbol that represents the amount of energy lost or gained in a reaction. +?H is endothermic (because it gains heat) -?H is exothermic (because it looses heat)

Exothermic: lower energy level at end; Endothermic: more energy at end; Activation energy is the energy requires to start the reaction.

Breaking bonds requires energy, this takes in heat: endothermic. Making bonds releases energy, this gives out heat: exothermic.

Surface area •Put a set mass of magnesium in hydrochloric acid •Time the reaction •Change the from of magnesium keeping the mass the same (powder, wire, strips) •The more surface area (the smaller the pieces of magnesium) the faster the reaction Concentration •Put a set mass of marble chips into dilute hydrochloric acid •Time the reaction •Change the ratio of water to hydrochloric acid •The more concentrated the hydrochloric acid (the lower the ratio of water) the faster the reaction Temperature •Put a set mass of magnesium powder into a set mass of hydrochloric acid •time the reaction •Carry out this reaction at different temperatures •The higher the temperature the faster the rate of reaction Catalyst •If you have hydrogen peroxide it will not decompose •If you put it with manganese dioxide it will decompose into water and oxygen •The manganese dioxide will be unaltered by the reaction •The more of the catalyst the faster the reaction

Higher temperature, more surface area, higher concentration, higher pressure and use of a catalyst all make a reaction faster.

Collision theory says that to react particles must: Collide with enough energy to react Collide in the right orientation to react (the more frequent the collisions, the more likely this is) Surface area •Particles collide more frequently if there is more surface area, as there is more contact between the reactants. Faster rate of reaction. Concentration/ pressure •There is more chance of particles colliding at a higher concentration/pressure, so they react more often. Faster rate of reaction. Temperature •Particles move about more and will collide more frequently the higher the temperature; react more often. Increases the rate of reaction. Catalyst •Provides an alternative pathway for the reaction to start which requires a lower activation energy.

explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy A catalyst provides an alternative route for the reaction to start, this route requires less energy to start the reaction.

Some reactions can happen both ways: the reactants can make the products and the products can make the reactants. This symbol shows that ?.

If you add water to copper sulphate you can make hydrated copper sulphate. If you remover the water from hydrated copper sulphate you can make copper sulphate. When heated, ammonium chloride splits into to hydrogen chloride and ammonia. Hydrogen chloride and ammonia can be reacted to make ammonium chloride.

Dynamic equilibrium is when a reversible reaction is happening both ways at the same time, at the same rate.

If you move the equilibrium, you change the rate of reaction. If the equilibrium moves to the right, you have more products. (the reactants are reacting faster) If the equilibrium moves to the left, you have more reactants. (the products are reacting faster) If you increase the pressure: the equilibrium will move to the side with least molecules. If you decrease the pressure: the equilibrium will move to the side with the most molecules. If you increase the temperature, there will be more products that are produced by an endothermic reaction. This is because the reaction is trying to use up the extra heat, and it does so by putting the energy into making bonds.