CHAPTER REFLECTION
Through the lecture, I have learnt the following topics:
The factors affecting rate of reaction (temperature, pressure, surface area, presence of catalyst, concentration)
Sampling: Small samples obtained while the reaction is quenched to ensure accuracy, and that any retrieval of sample is not impacted by its time interval. The sample is chemically analysed through methods such as titration.
Continuous: Physical property of the experiment is monitored without quenching or taking samples. This can be done through colourimetry, electrical conductivity, measuring pressure and volume changes, using gas syringe and dilatometer.
Rate of reaction can be measured by drawing tangents to a graph and calculating its gradient.
The reaction orders consist mostly of zeroth, first and second order.
The rate-concentration graph:
Zeroth order: Straight horizontal line
First order: Straight line with (+) gradient passing through O
Second order: Positive quadratic curve passing through O
7. The concentration-time graph:
Zeroth order: Straight line with (-) gradient
First order: Curve with negative gradient with decreasing magnitude, constant half life
Second order: Similar to first order but starts off more steep and ends at higher [R] value. Half life is not constant but increasing
8. The reaction equation cannot be determined by the overall stoichiometric reaction, and can only be determined through experimental means by changing the concentration of one reactant and observing how it affects the reaction rate (which order).
Rate-determining Step
Slow step of reaction (usually in the beginning)
Determines rate equation
Rate equation follows stoichiometric equation of slow step
Homogeneous Catalyst
Ester hydrolysis (H+ aq)
H2O2 breakdown (I- aq)
S2O8 2- + 2I- → 2SO4 2- + I2 (Fe 3+)
Changes in oxidation number, but catalyst reformed
Heterogeneous Catalyst
Haber process (Fe)
Catalytic converters (Pt)
Steps:
Diffusion and adsorption
Reaction
Desorption
Diffusion away