3.2.5.6 Catalysts Flashcards

1
Q

What is a homogeneous catalysts?

A

Where it is in the same phase as the reactants

The reaction proceeds through an intermediate species

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2
Q

What is a heterogeneous?

A

Where it is in a different phase to the reactants

The reaction occurs at active sites on the surface of the catalyst

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3
Q

What is a phase?

A

The state of matter

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4
Q

How do heterogeneous catalysts work?

A

Catalytic action occurs on the solid surface which remains in place so the catalyst is not lost and does not need to be seperated from the products

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5
Q

How do you make heterogeneous catalysts more efficient?

A

Spread the catalyst on an inert support medium to increase the surface to mass ratio
Increase the surface area

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6
Q

Why do catalysts not last forever?

A

The surface becomes covered with unwanted impurities which is called poisoning
The finely divided catalyst may gradually be lost from the support medium

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7
Q

What is the catalyst for the Haber process?

A

Iron in the form of pea-sized lumps

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8
Q

What is the equation for the Haber process?

A

N2 (g) + 3H2 (g) =(reversible reaction)= 2NH3 (g)

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9
Q

What is the contact process?

A
It produces sulfuric acid
2SO2 + O2 = 2SO3
Catalysed by vanadium oxide (V2O5)
SO2 + V2O5 = SO3 + V2O4
2V2O4 + O2 = 2V2O5
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10
Q

Does the destruction of the ozone layer involved a homogeneous or heterogeneous catalyst?

A

Homogeneous

A ClO radical intermediate is formed

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11
Q

What are the reactions involved with I- and S2

O8(2-)?

A

S2O8(2-) + 2I- = 2SO4(2-) + I2

Peroxidedisulfate ions oxidises iron (II) to iron (III):
S2O8(2-) + 2Fe(2+) = 2SO4(2-) + 2Fe(3+)

Fe(3+) oxidies I- to I2, regenerating the Fe(2+) ions so that none are used up:
2Fe(3+) + 2I- = 2Fe(2+) + I2

Iron gives an ion to the peroxidedisulfate and takes one back from the iodide ions

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12
Q

What is autocatalysis?

A

When one of the products of the reaction is a catalyst for the reaction
So the reaction starts slowly then speeds up as more product is produced

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