kinetics

What is the definition of reaction rate?

The change in concentration of a reactant or product over time

Equation for rate of reaction?

Amount of reactant used up or product formed/ time

3 ways to measure reaction rate?

1. Measuring a decrease in mass- for reactions that produce gases you can measure the rate by observing the decrease in mass over time. As gas is released the mass decreases. Should be conducted in a fume cupboard

2. Measuring the volume of gas given off- you can use a gas syringe to measure the volume of gas produced over time

3. Timing how long a precipitate takes to form- this approach is suitable when the product of the reaction is a precipitate, measure how long it takes for a mark to become obscured by the precipitate, always use the same observer and reference mark for consistency

What does collision theory state?

That for a reaction to take place between particles they must collide with the correct orientation and at least a minimum amount of kinetic energy

What is activation energy?

The minimum energy required for a collision to be effective

Why does increased surface area increase rate of reaction?

More particles on the surface are available to collide and react which leads to a higher frequency of effective collisions between the solid and other reactants

Increasing concentration increases rate of reaction why?

The particles will on average be closer together so will collide more frequently increasing the number of effective collisions

Increasing pressure increases rate of reaction why?

Raising pressure forces the gas particles closer together and so collide more frequently increasing the number of effective collisions

Increasing temperature increases rate of reaction why?

Raising temperature increases the kinetic energy and speed of the particles, as the particles move faster they collide more frequently resulting in an increased frequency of collisions, additionally the increased kinetic energy means more particles have the necessary energy to overcome the activation energy resulting in a greater proportion of effective collisions

Adding a catalyst increases rate of reaction why?

A catalyst provides an alternative pathway or mechanism for the reaction that has lower activation energy meaning particles require less kinetic energy to react, more particles have the activation energy leading to an increased number of effective collisions

What does the maxwell boltzmann distribution curve show about molecular kinetic energies in gases?

Some molecules move slowly because they have low kinetic energy, others move very fast due to their high kinetic energy, the majority of molecules however have moderate kinetic energies and speeds, only molecules with kinetic energies greater than or equal to the activation energy have sufficient energy to react when they collide

What does the maxwell boltzmann distribution curve peak represent?

The most probable kinetic energy level among the molecules

Where is the average energy of molecules shown in the maxwell boltzmann distribution curve show?

Slightly right of the peak

How does a temperature rise affect the maxwell boltzmann distribution curve?

As temperature rises a greater number of molecules attain kinetic energy above the activation energy. The distribution curve therefore shifts to the right. The total number of molecules remains constant so the area under the curves remain the same resulting in a lower peak height

What is a catalyst?

A substance that increases the rate of a chemical reaction by providing an alternative route for the reaction that has a lower activation energy

How does a catalyst change the maxwell boltzmann distribution curve?

By lowering the activation energy