Reactions and Acids and Alkalis

Rate of Reactions depend on: Temperature Concentration Catalyst Surface Area of solids

Rate of Reactions

The rate of a reaction can be measured by the rate at which a reactant is used up, or the rate at which a product is formed.

Chemical reactions can only happen if reactant particles collide with enough energy. The more frequently particles collide, and the greater the proportion of collisions with enough energy, the greater the rate of reaction.

3 Ways Rate of reaction can be MeasuredPrecipitation When the product is a precipitate which clouds the solution Observe a mark through the solution Time how long it takes to disappear The quicker it disappers the quicker the reaction only works when initial solution is see through result is subjective The Volume of Gas Given off Using a gas syringe to measure the volume of gas given off The more gas given off during a time the faster the reaction A graph could be ploted to see this Gas syringes are usually quite accurate Change in Mass Usually gas given off measuring the speed of a reaction that produces a gas measuring the speed that a reaction produces a gas Can be carried out on a mass balance a gas is released mass goes down the quicker the reading drops The faster the reaction most accurate though you are loosing your product

Hydrochloric Acid and Marble Chips Measure volume of gas released with a gas syringe take readings at regular intervals Make a table of readings Plot them on a graph Repeat the experiment But the marble chips more smashed up Then repeat with powered chalk  Instead of Marble chips

This shows the effect of using finer particles of solid Means larger surface area More frequent collisions The rate of reaction is faster

Reaction of Magnesium Metal with Dilute Hydrochloric Acid Good for measuring effect of increased concentration This reaction gives of hydrogen gas Can be measured using a mass balance

Shows the effect of using more concerntrated acis solutions Take readings at regular time intervaks Put results in a table]Work out the loss of mass for each reading lot graph Repeat with more concentrated acid Keep the same amount of magnesium Volume of acid must be kept the same too The higher the concerntrated the faster the reaction

Sodium Thiosulfate and Hydrochloric acid to produce Cloudy Precipitate Both reactants are clear They react to form yellow precipitate Involves watching black mark disappear through cloudy sulphur and timing Can be repeated at different temperatures Best way is to use a water bath depth of liquid must be kept the same Results will show that a higher temperature means a faster reaction

Decomposition of Hydrogen Peroxide To show effect of catalysts using manganese oxide as a catalyst oxygen is given off Measured using a gas syringe Better catalysts give a quicker reaction

More Collisions increase Rate of ReactionEffects of temperature, Concentration and Surface area on the rate of reaction can be explained in terms of how often reacting particles collide sucessfully

Higher Temperature Increases collisions Particles move quicker So they collide more often

Higher Concerntration (or pressure) increases collisions There are more particles Collisions more likely

Larger Surface Area Increases Collisions if it is a solid Breaking it up will increase surface area Means that particles around it have more area to work on More frequent collisions

Faster Collisions increase rate of reactions Increasing temperature causes faster collisions Reactions only happen if particles collide with enough energy The minimum amount of energy needed is Activation energy At higher temperatures there will be more particles with enough energy

Catalysts Speed up Reactions Catalyst is a substance that speeds up reactions without being used up Solid catalysts give reacting particles surface area to stick to This increases the number of successful collisions

Catalysts help to reduce costs in industrial reactions Increase rate of reactions Save money The plant doesn't need to operate for as long A catalyst allows the reaction to take place at lower temperatures Reducing energy cost Good for sustainable development Catalysts can be expensive But they don't get used up Need different catalysts for different reactions Catalysts can stop working if they come into contact with impurities

Exothermic - Heat is given out Transfers energy to the surroundings usually in heat Usually shown trough a rise in temperature combustion - burning fuels Neautralisation reactions Oxidation reactions everyday uses - hand warmers

Endothermic - heat is taken in Takes in energy from surroundings Usually I heat Shown through a fall in temperature less comman thermal decompostitions sports injury packs - take in heat release cold

Reversible Reactions - can be both will be exothermic in one direction will be endothermic in the other the energy absorbed in the endothermic reaction is equal to the energy released during the exothermic reaction

pH scale goes from 0-14

Indicator - a dye that changes colour Universal indicator is a combination of dyes which gives colours as shown above Good for estimating pH of a solution

Acids and Bases Neutralise each otherAcids pH less than 7 form H+ ions in water Bases pH greater than 7 Alkali is a base dissolved in water From OH+ ions in water

State symbolsTell us the physical state(s)  Solid(l)  Liquid(g)  Gas(aq)  Dissolved in Water

Rate of Reactions

Rate of Reaction Experiments

Collision Theory

Energy Transfer in Reactions

Acids and Alkalis