Kinetics Flashcards
Define activation energy
The minimum energy that a particle needs in order to react. Or the energy difference between the reactants and the transition state.
Describe enthalpy diagrams
Enthalpy is y axis, extent of reaction is x axis. Horizontal line for reactants on left higher than line for products on the right for exothermic reactions (opposite for endothermic). Transition state is horizontal line above and between line for reactants and products. Curved line from reactants, touching transition state, back down to products.
How does increasing the concentration of reactants increase the rate of reaction?
If more particles in given volume then collisions more likely and therefore more frequent so the reaction rate is faster.
How does increasing the pressure of reactants increase the rate of reaction?
More molecules or atoms in given volume so collisions more likely and therefore more frequent and reaction rate is faster. Same as concentration.
How does increasing the surface area of reactants increase the rate of reaction?
The greater the total surface area of a solid, the more of its particles are available to collide with the other reactants (more sites for reaction) so there are more frequent collisions so the reaction rate is faster.
How does increasing the temperature of reactants increase the rate of reaction?
It increases the speed of the molecules and therefore their energy. This means a lot more particles have at least the activation energy so a higher percentage of collisions will be effective and result in s reaction. A small increase has a disproportionately large increase on the rate of reaction.
Describe the Maxwell-Boltzmann distribution curve at room temperature
Fraction of particles with energy is y axis. Energy is x axis. Line is steep at start up to highest point which is the most probable energy. Just below the peak to the right is the average energy. Curves down with ever decreasing gradient but doesn’t touch x axis. Activation energy is quite far to the right of the average energy.
How do catalysts increase the rate of reaction?
They provide a different pathway for the reaction which has a lower activation energy. This means a lot more particles have at least the activation energy so a greater proportion of the collision between reactants will be successful so the reaction rate is faster.
How does a catalytic converter work?
It is a honeycomb structure made of ceramic material coated in rhodium and platinum as catalysts. The gases first form weak bonds with the metal atoms of the catalyst (adsorption). This holds the gases in just the right position to react with each other. The gases react on the surface. The products then break away from the metal atoms (desorption) freeing up room for more gases to react.
Define catalyst
A substance that increases the rate of a chemical reaction but is not changed in chemical composition or amount.
Things to remember when investigating how rate of reaction changes with temperature.
Reactants should all be at the temperature being investigated. All other variables that affect rate of reaction (e.g concentration) should be kept the same. Have same reference point of stage of reaction for each repeat.
