rates of reactions

what reactions are fast?

acid base reactions

what reactions are slow?

reactions involved in breaking covalent molecular bonds, particularly in large molecules

how can the rate of reaction be determined?

by measuring either directly or indirectly, the formation of products or the depletion of reactants over time

what factors can be measured to determine the rate of reaction?

• mass lost by reagent

• mass gained by product

• volume of gas

• pressure of gas

• colour intensity

• solution concentraiion

• pH

The number of collisions that take place are… however…

large however the vast majority of these collisions are not successful and do not result in the formation of products

what is the collision theory?

the collision states that for a chemical reaction to take place the particles must collide with the correct orientation and sufficient energy. if either of these criteria are not met, the collision will not be successful and no chemical change will occur

what happens if the particles collide with not the right orientation?

then, the breaking of existing bonds and the formation of new ones do not occur and the particles will simply bounce off each other and no reaction occurs

what would effect the successful collisions two particles have concerning their orientation?

large or complex molecules where the reactive sites represent only a small part of the whole molecule only have a very small number of collisions with appropriate orientation this tends to result in a slow reaction rate. similarly, molecules with extensive structures where the reactive sites are obscured with other reacting particles dont always react to any appreciable extent

why is kinetic energy important in successful collisions?

when two reactant particles collide, even if they are in the correct orientation, they still need tp have a certain amount of kinetic energy for the collision to be successful and generate products. This energy is a requirement of the bond breaking and formation process

what is the formula for kinetic energy

KE = (1/2)mv^2 where KE is kinetic energy, m is mass, and v is velocity

what does a Maxwell boltzmann distribution curve represent?

it shows the range of kinetic energies possessed by the particles in a a substance at a particular temperature

what is on the x and y axis of a Maxwell botzemann graph

x axis is the kinetic energy, and y is the number of particles with kinetic energy

will the line on a Maxwell Boltzmann distribution curve ever reach zero ?

no, this is because there will always be a chance of some particles possessing extremely high kinetic energies

what does the line in a energy distribution curve mean?

the area beneath the curve represents the total number of particles in a sample, with the maximum on the graph does not show the maximum energy but the greatest number of particles in the substance at that existing with that kinetic energy

only particles that have kinetic energy greater or equal to a certain value will…

successfully collide to generate products, this certain value is known as the activation energy

what does the activation energy represent?

the activation energy represents the minimum amount of energy that is required to break the existing chemical bonds, allowing for products to be made

what is the transition state?

is the highly energised and highly unstable arrangement of reactant particles where the bond breaking and formation takes place

what is the enthalpy of an exothermic reaction?

the enthalpy is negative as this reaction releases energy into the surroundings

what is the reaction of an endothermic reaction?

the enthalpy is positive as the reaction absorbs energy from the surroundings

what does the magnitude of a reactions activation energy determine?

it determines the ease with which a given reaction occurs. A reaction that has been determined to be viable may not happen because of its high activation energy

what factors can change the rate of reaction in a chemical reaction?

• surface area of solid reactions

• concentration of reactants in a solution

• gas pressure

• temperature

• presence of a catalyst

in any given reaction mixture, only a certain percenntage of the collisions are..

successful

how does surface area effect reaction rate?

when a solid is involved in a reaction, only the particles at the surface of the solid are available to collide with other reactant particles. the number of particles at he surface depends on the surface area of the substance

how can energy be described?

it can be describes as the capacity to do work or cause change

the amount of energy present is always

constant

What is the law of conservation of energy?

Energy can neither be created nor destroyed; it can only be transformed from one form to another or transferred between objects. The total energy within an isolated system remains constant, although it may change forms. The total energy of the system and its surroundings stays constant.

what is enthalpy

is the ear of energy present in a substance

weak bonds hold more…

chemical potental energy than strong ones

why does the temperature of a system rise or fall in a system after a reaction?

during a chemical change some bonds are broken and new Onnes are formed and so there will inevitably be a change (increase or decrease) in the amount of stored chemical potential energy. As this change must be conserved, any change in chemical potential energy must be balanced. by an opposite charge in some other form of energy, usually particle kinetic energy (heat)

heat always flows from

hotter regoins to cooler oes