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1

rate of reaction

the change in concentration per unit time of any one reactant or product

2

factors affecting rate

nature of reactants
particle size
concentration
temperature
catalysts

3

rate graphs

concentration inversely proportional to time

temp inversely proportional to time

4

catalyst

a substance that alters the rate of reaction but is not consumed in the reaction

5

homogeneous catalysis - when it occurs

occurs when reactants + catalyst are in the same phase

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heterogeneous catalysis - when it occurs

occurs when reactants + catalyst are in different phases

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factors that affect rate of reaction

concentration
area (surface area)
temperature
nature of reactants

8

nature of reactants

covalent compounds
ionic compounds

9

covalent compounds

-slow reactions
-bonds broken before new ones formed

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ionic compounds

-fast reactions
-oppositely charged ions come together

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general rules for graphs

-use graph paper
-label both axis with title and units
-plot points accurately
-if two things to plot on graph, put both on same graph if they tell you to. Draw in diff colours and write a key outside
-decrease in graphs has -y axis

12

instantaneous

means "at an instant", not referring to speed of reaction

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temperature

-the hotter the temp, the more energy the particles have
-more energy - faster the particles move
-more effective + frequent collisions + reaction occurs quicker
-higher the temp, shorter the reaction time

14

concentration

-increasing concentration, increases rate of reaction
-for H₂O₂ - inc conc, inc amount of product (gas) produced, as it is the only reactant present
-for hydrochloric acid + sodium thiosulphate - inc conc, causes same amount of gas to be produced but in shorter time

15

eg of catalyst

hydrogen peroxide decomposes into water + oxygen at room temp, the addition of manganese dioxide as a catalyst causes hydrogen peroxide to decompose faster

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properties of catalyst

-remains chemically unchanged at end of reaction
-only needed in small amounts
-specific - work for one reaction but not another
-in equilibrium reactions - a catalyst helps equilibrium to be achieved quicker

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types of catalysis

homogeneous
heterogeneous
autocatalysis

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homogeneous catalysis

both reactants + catalyst are in same physical state
no boundary between reactants + catalyst

eg. both are liquids - aqueous potassium iodide + hydrogen peroxide, potassium iodide breaks H₂O₂ into water and oxygen

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heterogeneous catalysis

reactants + catalyst are in diff physical state
there is a boundary between reactants + catalyst

eg. hydrogen peroxide (liquid) + manganese dioxide (solid) or oxidation of methanol by platinum catalyst

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autocatalysis

where one of the products of a reaction catalyses the reaction

eg. reduction of manganate (VII)

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reduction of manganate (vii)

MnO₄⁻ + 8H⁺ + 5Fe²⁺ --> Mn²⁺ + 5Fe³⁺ + 4H₂O

Mn²⁺ catalyses the reaction
purple colour decolorises slowly
decolorising speeds up due to Mn²⁺ ions produced, catalysing reaction

22

catalytic converters

exhaust fumes are a major source of air pollution. They can release these in the atmosphere:
-Carbon monoxide (CO)
-nitrogen monoxide (NO)
-Nitrogen dioxide (NO₂)
-unburned hydrocarbons

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carbon monoxide

formed from incomplete combustion of hydrocarbons in fuels
-highly toxic in blood stream
-colourless, odourless, tasteless gas

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nitrogen oxide

formed when atmospheric nitrogen and oxygen react at high temp of spark plug
-then reacts w/ more oxygen to form nitrogen dioxide
-nitrogen dioxide reacts w/ water to form nitric acid, leads to acid rain

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unburned hydrocarbons

arise from unburned fuel + gives rise to smog

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catalytic converter

converts environmentally harmful gases into harmless gases

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what catalytic converter consists of

-thin coating of platinum, palladium, thiodium on ceramic/metal honeycomb inside stainless steel case
-catalysts spread over surface of honeycomb which has large surface area
-mixture of hot harmful gases then converted into harmless products

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reactions that take place in catalytic converter

2CO + 2NO --(Pt/Pd/Rh)--> 2CO₂ + N₂

unburned hydrocarbons react with oxides of nitrogen to form carbon dioxide, nitrogen + water which occur naturally in the air

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replacement

catalytic converters will need to be replaced due to poisoning of catalyst mainly from lead. When the converter is changed it is possible to recover most of the catalyst + recycle it

30

advantage of catalytic converters

-decrease in carbon monoxide emissions, nitrogen oxide emissions, smog, acid rain
-increase in air quality