11A - Kinetic Rates Flashcards
What does the rate of reaction refer to?
The change in the amount or concentration of a reactant or product per unit time.
What are the units for the rate of reaction?
mol dm^-3 s^-1.
What are the methods to measure the rate of reaction?
-Mass lost over time.
- Volume of product produced over time.
- Color changes, including by the use of colorimetry.
- pH changes over time.
- Changes in electrical conductivity.
How can the rate of reaction be calculated?
Rate of reaction (mol dm^-3 s^-1) = Δ[Reactants/Products] / Δtime
When reactants are used, a negative sign needs to be used so that final rate value is positive.
Why cannot the method of change in mass over time be used for an experiment releasing hydrogen gas?
Hydrogen has a low relative molecular formula so the mass changes over time will be very small leading to significant measurement uncertainties.
What are the advantages of using a gas syringe than collecting over water into measuring cylinder?
- There’s a greater degree of precision in gas syringes.
- Some gases are water soluble such as SO2 so you can only use a gas syringe.
What are the advantages of using method of collecting over water into measuring cylinder than gas syringe?
- If the gas volume is large, then difference of degree of measurement uncertainty becomes too small.
- The water in measuring cylinder can be saturated with the gas that will be collected so that it won’t dissolve in it.
What is the rate expression for a directly proportional relationship between rate and concentration?
Rate ∝ [D] or Rate = k[D].
What does the rate expression Rate = k[D] mean?
It means that if the concentration of D is doubled, the rate doubles; if concentration halves, the rate also halves.
What is the rate equation for the reaction A (aq) + B (aq) → C (aq) + D (g)?
Rate of reaction = k[A]^m[B]^n.
How are rate equations determined?
Rate equations can only be determined experimentally and cannot be found from the stoichiometric equations. This is due to the following reasons:
Complex Reaction Mechanisms
Reaction Orders
Rate constants
Catalyst and Reaction Conditions
What do [A] and [B] represent in the rate equation Rate = k[A]^m[B]^n?
[A] and [B] are the concentrations of the reactants.
What do m and n represent in the rate equation Rate = k[A]^m[B]^n?
m and n are orders with respect to each reactant involved in the reaction.
Can products and catalysts feature in rate equations?
Yes, products and catalysts may feature in rate equations.
Do intermediates feature in rate equations?
No, they don’t.
