5.1- COLLISION THEORY Flashcards
What is kinetics the study of?
factors that affect rates of chemical reactions- how quickly they take place
How can reactions be sped up or slowed down?
by changing the conditions
For a reaction to take place between two particles, what must they do?
must collide with enough energy to break bonds
Where must the collision take place for a reaction to take place between two particles?
must take place between parts of molecule that are going to react together, so orientation also has part to play
What do you need to have a lot of collisions? (collision theory)
need a lot of particles in small volume
What do the particles need to be doing to have enough energy to break bonds? (collision theory)
need to be moving fast
What do you need for a fast rate of reaction? (collision theory)
need plenty of rapidly moving particles in a small volume
Do most collisions between molecules/ other particles lead to reaction?
no
Why do most collisions between molecules/ other particles not lead to reaction?
either do not have enough energy, or they’re in wrong orientation
What factors will increase the rate of a reaction? (5)
increasing temp increasing concentration of solution increasing pressure of gas reaction increasing SA of solid reactants using catalyst
How does increasing the temperature increase ROR?
increases speed of molecules, in turn increases energy + number of collisions
How does increasing the concentration of solution increase ROR?
if there are more particles present in given volume then collisions more likely + reaction rate would be faster
but as reaction proceeds, reactants used up + their concentration falls
so in most reactions ROR drops as reaction goes on
How does increasing the pressure of gas reaction increase ROR?
has same effect as increasing conc. of solution- more molecules/ atoms in given volume so collisions more likely
How does increasing the SA of solid reactants increase ROR?
greater the total SA of solid, more of its particles available to collide with molecules in gas/ liquid
means breaking solid lump into smaller pieces increases ROR as there are more sites for reaction
How does using a catalyst increase ROR?
catalyst is substance that can change rate of chemical reaction without being chemically changed itself
What must molecules have for a collision to result in a reaction?
certain minimum energy, enough to start breaking bonds
What is the minimum energy needed to start a reaction called?
activation energy
How long would it take an exothermic reaction with a large activation energy to happen at room temp?
extremely slowly
Why would an exothermic reaction with a large activation energy happen extremely slowly at room temp?
very few collisions will have sufficient energy to bring about reaction
How long would it take for an exothermic reaction with a small activation energy to happen at room temp?
will happen rapidly
Why would an exothermic reaction with a small activation energy happen rapidly at room temp?
many collisions will have enough energy to bring about reaction
What is the species that exist at the top of the curve of an enthalpy diagram called?
transition state or activated complex
What is happening to the species at the top of the curve of an enthalpy diagram (transition state/ activated complex)?
some bonds in process of being made + some bonds in process of being broken
What is the energy of the activated complex like?
has extra energy + is unstable
What is the energy of reactants + products in an endothermic reaction?
products have more energy than reactants
