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74 Cards in this Set
- Front
- Back
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How are irreversible reactions represented? |
By a single arrow |
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How is a state of dynamic equilibria established? |
Reversible reaction carried out in closed container so reactants and products can't escape |
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What is assumed when a reaction is in a state of dynamic equilibrium? |
Forward/ backward reaction occur at same rate Concentration of reactants + products remain constant |
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When on the graph does concentration of reactants + products remain constant? |
When the lines level off |
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How is a reaction in equilibrium described? |
Forward reaction starts off fast but slows as reactants get less concentrated |
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How is an initial reaction in equilibrium described? |
No backward reaction but as products formed it will get faster |
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When has the reaction reached equilibrium? |
When the rate of backward and forward reactions are equal |
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What is Le Chateliers principal? |
If factor affecting position of equilibrium is altered, position of equilibrium shifts to oppose change |
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How does the position of equilibrium change when concentration changes? |
A + B <=> C + D Equilibrium will shift to oppose the change to decrease/increase concentration of A so equilibrium shifts to right/left |
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What is the first stage of calculating equilibrium change when temperature changes? |
Calculate if heat is given / taken |
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How does the position of equilibrium change when temperature increases? |
Equilibrium will shift to oppose change so shifts to endothermic direction so shifts to left/right |
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How does the position of equilibrium change when pressure increases? |
Equilibrium shifts to oppose change so shifts to side with fewest moles of gas so shifts to the right/left |
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How does the position of equilibrium change when a catalyst is added? |
It will alter rate but no equilibrium so the forwards and backwards reaction will be affected equally |
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Why is 700-750k used as a compromise temperature in the Haber process? |
At lower temp, equilibrium shifts to exothermic direction to right to oppose change and increase yield of NH3 but too low temp decreases rate of reaction so NH3 produced too slowly |
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Why is 200atm used as a compromise pressure in the Haber process? |
At higher pressure, equilibrium shifts to side with fewest moles of gas (the right) to oppose change and increase yield of NH3 and rate but is expensive. |
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What is the effect of a catalyst in the Haber process? |
Causes equilibrium to be reached faster but won't change the position of equilibrium so won't affect yield of ammonia |
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Kc = |
[C]^c × [D]^d / [A]^a × [B]^b |
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What do square brackets show? |
Concentration |
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How do you calculate the concentration of the components of the reaction? |
Reactants Initial Change Equilibrium |
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When can you cancel volume terms? |
If the number of moles of reactants produces the same number of moles of products |
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What does the value of the equilibrium constant depend upon? |
The position of equilibrium |
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What is the value of Kc for the reverse reaction? |
Inverse of the reaction |
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What is the effect of temperature on Kc? |
Changing the temperature changes the value of kc |
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What does the value of KC depend on? |
Whether the reaction is exothermic or endothermic |
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What is the effect of increasing temperature on a forward exothermic reaction? |
Shifts equilibrium to the left and the value of Kc decreases |
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What is the effect of increasing temperature on a forward endothermic reaction? |
Shifts equilibrium to the right and the value of Kc increases |
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What is the effect of concentration/p pressure on Kc? |
According to Le Chatelier, if the concentration/pressure of a reactants or product changes the equilibrium shifts to oppose the change so the ratio of products to reactants is always the same. |
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What is the effect of a catalyst on Kc? |
Reduce time taken for a reaction to reach equilibrium but have no effect upon the position of an equilibrium so doesn't affect the value of Kc |
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What is the only thing Kc is effected by? |
Temperature |
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What is a redox reaction? |
A reaction in which one substance is reduced and another is oxidised. |
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Lead oxide + carbon --> |
Lead + Carbon Dioxide |
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What is reduction? |
Loss of oxygen Gain of hydrogen Gain of electrons |
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What is oxidation? |
Gain of Oxygen Loss of Hydrogen Loss of Electrons |
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In a reaction between magnesium and oxygen, what is the reducing agent? |
Magnesium - has been oxidised so caused the oxygen to be reduced |
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In a reaction between magnesium and oxygen, what is the oxidizing agent? |
Oxygen - has been reduced so caused the magnesium to be oxidized |
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What is a reducing agent? |
Reducing agents donate electrons to another species and are themselves oxidised |
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What is an oxidizing agent? |
Oxidizing agents accept electrons from another species and are themselves reduced |
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What are common reducing agents? |
Zinc (or any metal) Hydrogen Carbon Sodium tetrahydridoborate |
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Why is any metal a good reducing agent? |
Always lose electrons when they react so tend to be good reducing agents |
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What are common oxidizing agents? |
Chlorine (any non-metal) Hydrogen Peroxide Potassium dichromate Concentrated sulfuric acid |
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Why is any non-metal a good reducing agent? |
Always gain electrons when they react so tend to be good oxidizing agents |
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What is the oxidation state of an atom? |
The charge the atom would have if all the bonding electrons go to the most electronegative atom |
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What is rule 1 of assigning oxidation states? |
The oxidation state of an atom in an element is always zero |
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What is rule 2 of assigning oxidation states? |
The oxidation state of a simple ion is its charge |
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What is rule 3 of assigning oxidation states? |
The oxidation state of fluorine in its compounds is always -1 as it is the most electronegative element |
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What is rule 4 of assigning oxidation states? |
The oxidation state of oxygen in its compounds is usually -2 except if bonded to fluorine or in peroxides or superoxides |
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What is rule 5 of assigning oxidation states? |
The oxidation state of hydrogen in its compounds is usually +1 except when bonded to a metal ion, in which case it is -1 |
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What is rule 6 of assigning oxidation states? |
The sum of the oxidation states of all the atoms in a compound is always zero |
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What is rule 7 of assigning oxidation states? |
The sum of the oxidation states in polyatomic ions is always the charge on the ions |
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What elements have a fixed oxidation state of +1 in compounds? |
Hydrogen Lithium Sodium Potassium |
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What elements have a fixed oxidation state of +2 in compounds? |
Magnesium Calcium Barium |
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What element have a fixed oxidation state of +3 in compounds? |
Aluminium |
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What elements have a fixed oxidation state of -2 in compounds? |
Oxygen |
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What elements have a fixed oxidation state of -1 in compounds? |
Fluorine |
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What element goes first when writing the formula of a compound? |
The element with a positive oxidation state |
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What is the maximum oxidation state an element can have equal to? |
The group number in the periodic table |
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What is the purpose of roman numerals? |
To indicate the OS of the atom with a variable OS |
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What are the roman numerals up to 7? |
1 I 2 II 3 III 4 IV 5 V 6 VI 7 VII |
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What is the purpose of half equations? |
To represent either the oxidation or the reduction |
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What must the two half equations must add up to? |
The balanced equation for the whole reaction |
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What happens to spectator ions in a half equation? |
They're ommited |
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What is an increase in oxidation state? |
Oxidation |
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What is a decrease in oxidation state? |
Reduction |
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What is the first step of writing half equations? |
Write down the formula for the reactants and products |
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What is the second step of writing half equations? |
Balance the atoms undergoing redox |
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What is the third step of writing half equations? |
Balance any oxygen atoms by adding water |
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What is step 4 of writing half equations? |
Balance any hydrogen atoms by adding H+ ions |
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What is step 5 of writing half equations? |
Balance the charge by adding electrons |
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What must the total number of electrons transferred be equal to? |
The total change in oxidation state |
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What must half equations show when being combined? |
Oxidation and reduction with equal number of electrons being lost and gained |
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Oxidation of ethanol to ethanal |
CH3CH2OH + [O] --> CH3CHO + H2O |
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Oxidation of ethanal to ethanoic acid |
CH3CHO + [O] --> CH3COOH |
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Oxidation of ethanol to ethanoic acid |
CH3CH2OH + 2[O] --> CH3COOH + H20 |
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Ethanal with Tollens' reagent |
Overall = 2[Ag (NH3)2]+ + CH3CHO + H2O --> CH3COOH + 2H+ + 2Ag + 4NH3 |
