Unit 6-Equilibria And Redox

Question 1

Reversible reactions and equilibrium

Answer 1

• shown by two arrows pointing in opposite directions
• means reaction is going both ways at all times, if reactions take place at the same rate the concentrations are static (point of equilibrium)
• equilibrium can be changed to affect amount of product formed on either side of the equation according to le chateliers principle
• adding a catalyst makes the reaction reach equilibrium faster

Question 2

industrial processes

Answer 2

• must consider the cost of running high temp/pressure reactions against the speed of the reaction, the yield and the potential to corrupt expensive catalysts
• if a product is exothermic, low temp shifts eq. towards it, however this also slows the rate of reaction
• if a product has fewer molecules it requires high pressure to shift eq. towards it, but this costs a lot
• recycling unreacted materials can make inefficient processes better

Question 3

the equilibrium constant

Answer 3

• Kc (equilibrium constant) = ([D]^d + [E]^e)/([A]^a + [B]^b)
• [x] means concentration of x in moldm^-3
• units can vary depending on how they cancel out in the formula
• Kc increases when more product is formed in equilibrium, it decreases when less product is formed
• the value of Kc isn’t affected by changes in concentration or addition of a catalyst

Question 4

factors that affect equilibrium

Answer 4

• if concentration or pressure increases, eq. shifts to the side that produces fewer molecules
• if temp increases, eq. shifts to endothermic side, and vice versa

Question 5

oxidation states

Answer 5

• the total no. electrons and atom donates or accepts in a reaction
• unreacted atoms have state of 0, atoms bonded to the same element also have state of 0
• compounds with neutral charges must have balanced oxidation states that cancel out between the atoms in it
• roman numerals are usually next to elements not in their normal state or that have multiple common states when written in formulas
• oxidation numbers in a compound should cancel out to the ionic charge of the compound, and they should be equal on both sides of an equation

Question 6

rules for oxidation states

Answer 6

• halogens always have -1, unless bonded to oxygen
• alkali metals always have +1
• oxygen has s state of +2, unless its in a peroxide then it is +1
• hydrogen is always +1 unless in a metal hydride, then it is -1

Question 7

redox reactions

Answer 7

• oxidation is the loss of electrons, reduction is the gain of electrons
• oxidising agents take electrons from other atoms, reducing agents give electrons to other atoms
• Redox is when one atom loses electrons (increases oxidising state) and another gains them (decreases oxidation state

Question 8

writing half equations

Answer 8

• used to show reduction and oxidation
• start writing by showing the change in oxidation state for every reactant, and balancing that equation using extra protons(H+) or electrons (e-)
• combine them by making all equations have the same number of electrons on either side so they can be cancelled out