Rates, equilibrium and pH

Define the rate of reaction?

• the change in the amount of reactants or products per time

State the unit for rate of reaction?

• mol dm^-3s^-1

what does the order of reaction tell you?

• it tells you how the reactant’s concentration affects the rate

Define overall order?

• the sum of the orders of all the different reactants

Give the rate equation?

• k[A]^m[B]ⁿ

What is k?

• the rate constant

What are ^m and ⁿ?

• the orders of the reaction with respect to the reactant A and reactant B

What does ^m tell you?

• how the concentration of reactant A affects the rate

What does ⁿ tell you?

• how the concentration of reactant B affects the rate

Define the half life of a reaction?

• the time it takes for half of the reactant to be used up

Define a 0 order reaction?

• where the reactants concentration is doubled and the rate stays the same

Define a 1 order reaction?

• where the reactants concentration is doubled and rate also doubles

Define a 2 order reaction?

• where the reactants concentration doubles and rate quadruples

What does the shape of a rate -concentration graph tell you?

• the order of the reaction

What does a horizontal line mean on a rate-concentration graph mean?

• changing concentration doesn’t change rate

• it’s order is therefore 0

What does a straight line mean on a rate concentration graph?

• the rate is proportional to [X]

• The order is 1

What does a curve mean on a rate concentration graph?

• the rate is proportional to [X]2

• it’s order is 2

What do colorimeters measure?

• the absorbency of a particular wavelength of light by a solution

State the steps to use a colorimeter?

• Set the colorimeter to measure the wavelength of light

• place a sample of distilled water into a curette and place into the colorimeter

• Set the absorbance to 0

• Take samples form the reaction mixture at regular intervals and measure the absorbance of each one using the colorimeter

What can be used to convert from absorbance to concentration?

• a calibration curve

If the half life of a reaction is known, state the equation which can work out the rate constant of a first order reaction?

Define the rate determining step?

• the step with the slowest rate

What 3 events must happen in order for a relation to occur?

• collide with each other

• Have sufficient energy to react

• Have the correct orientation

What does the Arrhenius equation link together?

• the rate constant (k) with activation energy(Ea) and temperature

State the formula and what the key components mean in the Arrhenius equation?

What does a larger activation energy result in?

• A slower rate of reaction

  • Not many of the reactant particles will have enough energy to reacts so only a few of the collisions will result in the reaction actually happening the the rate of reaction will be slow