What is a catalyst and main criteria for catalysis surface area
Answers
Key points
A catalyst is a substance that can be added to a reaction to increase the reaction rate without getting consumed in the process.
Catalysts typically speed up a reaction by reducing the activation energy or changing the reaction mechanism.
Enzymes are proteins that act as catalysts in biochemical reactions.
Common types of catalysts include enzymes, acid-base catalysts, and heterogeneous (or surface) catalysts.
Introduction: A kinetics thought experiment
Your brain is powered by the oxidation of glucose. The oxidation of glucose can be represented as the following balanced chemical reaction:
\text C_6 \text H_{12} \text O_6(s)+6\text O_2(g) \rightarrow 6\text C \text O_2(g) + 6\text H_2 \text O(l) + heat\quad\quad{\Delta\text G^\circ \,\text {at }25\,^\circ \text C=-2885\,\dfrac{\text{kJ}}{\text{mol}}}C
6
H
12
O
6
(s)+6O
2
(g)→6CO
2
(g)+6H
2
O(l)+heatΔG
∘
at 25
∘
C=−2885
mol
kJ
C, start subscript, 6, end subscript, H, start subscript, 12, end subscript, O, start subscript, 6, end subscript, left parenthesis, s, right parenthesis, plus, 6, O, start subscript, 2, end subscript, left parenthesis, g, right parenthesis, right arrow, 6, C, O, start subscript, 2, end subscript, left parenthesis, g, right parenthesis, plus, 6, H, start subscript, 2, end subscript, O, left parenthesis, l, right parenthesis, plus, h, e, a, t, space, space, delta, G, degree, space, a, t, space, 25, space, degree, C, equals, minus, 2885, space, start fraction, k, J, divided by, m, o, l, end fraction
Without this reaction, learning chemistry would be much harder. Luckily, the oxidation reaction is thermodynamically favored at 25\,^\circ \text C25
∘
C25, space, degree, C since \Delta\text G^\circ<0ΔG
∘
<0delta, G, degree, is less than, 0.
a slice of a dark grape, about 5 mm thin and seen against a window
a slice of a dark grape, about 5 mm thin and seen against a window
Did you know that glucose was first isolated from raisins? Image from Wikimedia Commons, public domain
Why don't we give it a try? Find some food that is nice and sugary, such as a raisin. Add some oxygen gas (i.e. hold it out in the air). What happens?
Do you notice a release of heat energy? The formation of water and a nice explosive poof of carbon dioxide gas?
Chances are, the raisin doesn't do much besides maybe dry out a little bit more. Even though the oxidation of glucose is a thermodynamically favorable reaction, it turns out that the reaction rate is really really really slow.
The rate of a reaction depends on factors such as:
Activation energy
Temperature: if you heat up the raisin to a high enough temperature, it will probably catch on fire and oxidize
These two factors are closely related: increasing the reaction temperature of the reaction increases the kinetic energy of the reactant molecules. This increases the likelihood that they will have enough energy to get over the activation barrier.