Reaction Rates Flashcards
What speeds up rate of reaction
Increasing temperature, pressure of a gas, concentration of a solution, surface area of a solid, and adding a catalyst.
How does increasing temp impact reaction rate?
More KE so particles move faster, more frequent successful collisions
How does increasing pressure impact reaction rate?
Particles are closer and collide successfully more frequently, increasing chance of a reaction.
How does increasing concentration impact reaction rate?
Increases. Particles are closer and collide more often, increasing chance of a reaction.
What is a sucsessful collision in a reaction?
Particles colliding at the right orientation to cause a reaction.
How does adding a catalyst impact reaction rate?
Increases reaction rate by providing an alternative pathway with a lower activation energy.
What are the two types of catalyst?
Homogeneous and heterogeneous
What is a homogeneous catalysts?
Same as phase as the chemicals in the reaction that it is speeding up.
These are usually aqueous in aqueous reactants.
Eg: using sulphuric acid to make an ester.
What is a heterogeneous catalysts?
Exists in a different phase from the chemicals in the reaction that it is speeding up.
Eg Haber process:
Na2+(g) + 3H2(g) —> 2NH3(g)
A solid iron catalyst is used.
How do you calculate rate of a reaction?
Amount of reactant used or product made/time
or
∆c/T
How does adding a heterogeneous catalyst increase reaction rate?
Increasing its SA means more particles can react with the catalyst at the same time.
Eg: Zeolite
How does adding a homogeneous catalyst increase reaction rate?
It forms intermediate species by combining with the reactants. This reacts to form the product and the catalyst is reformed.
Why does reaction rate slow?
Because the reactants are used up. The concentration decreases, decreasing the frequency of successful collisions.
The SA also decreases.
How do you calculate rate from a graph?
By measuring the gradient of a tangent at any time. ∆y/∆x
Eg a tangent at time = 0 (by extending it to the x axis)
ALL RATES NEED TO BE POSITIVE.
How can rates be measured in experiments?
- Time for a precipitate to form. (disappearing cross). The issues is it’s difficult to know exactly when. Try use same observer to reduce error.
- Amount of mass lost over specific time (when reaction produces gas). If toxic gas, use fume cupboard.
4.Volume of gas produced over amount of time using gas syringe. Use when mass of gas is negligible or very low density.
