6 and 7

Question 1

Definition of exothermic

Answer 1

when energy is lost from the system to the surroundings, in form of heat and is shown in the rise of temperature in the surroundings

Question 2

definition of endothermic

Answer 2

takes in energy from surroundings to system, in form of heat and is shown in the fall of temperature in the surroundings

Question 3

exothermic
energy in reactants ? products
bonds: broken ? made

ΔH = +/- ve

Answer 3

Energy in reactants > products

• products have less chemical energy than the reactants
• overall the temperature increases as energy is lost to the surroundings
  E: reactant ➝ surroundings

bonds: broken < made
Bond MAKING

ΔH (enthalpy - heat content in the system) = -ve for exothermic as energy is lost

Question 4

endothermic
energy in reactants ? products
bonds: broken ? made

ΔH = +/- ve

Answer 4

Energy in reactants < products

• overall the temperature decreases
  E: surroundings ➝ reactants

Bond BREAKING

ΔH (enthalpy - heat content in the system) = +ve for endothermic as energy is gained

Question 5

Give 3 examples of exothermic reaction

Answer 5

• combustion
• neutralisation
• most oxidation reactions
• rusting iron

Question 6

Give examples of exothermic reaction

Answer 6

• thermal decomposition
• reaction of citric acid and sodium hydrogencarbonate
• photosynthesis

Question 7

definition of a catalyst

Answer 7

• a substance that speeds up the rate of reaction
• remains chemically unchanged
• by providing an alternative route with a lower activation energy

Question 8

energy change equation

Answer 8

break - make

\+ve = endothermic
-ve = exothermic

Question 9

complete combustion reaction

Answer 9

excess of oxygen

hydrocarbon/fuel + O2 -> CO2 + H2O

Question 10

incomplete combustion reaction

Answer 10

oxygen deficient environment

hydrocarbon/fuel + O2 -> CO + H2O

Question 11

activation energy

Answer 11

minimum amount of energy needed to break bonds in reactants and start the reaction

Question 12

rate of reaction definition + formula

Answer 12

how fast the reactants are changed into products

amount of reactant used or formed/time

Question 13

enzyme definition

Answer 13

biological catalyst (fermentation reaction)

Question 14

photochemical reactions examples

Answer 14

started by energy in the form of light

substitution reaction of hydrocarbons with chlorine
photographic negatives
photosynthesis

Question 15

photosynthesis reaction

Answer 15

carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2 + energy
(light)
energy absorbed by chlorophyll

Question 16

photographic negatives

Answer 16

AgCl -(light)-> Ag + Cl

Question 17

redox reaction definition

Answer 17

in terms of electron transfer, a redox reaction is a reaction in which electrons move from oxidised species to reduced species

Question 18

oxidising/reducing agent

Answer 18

oxidising agent oxidises another substances during a redox reaction - the one which is reduced, gains e-

Question 19

acidified potassium manganate (VII)

Answer 19

KMnO4 oxidising agent
MnO4 - ion is reduced to Mn2+

• purple to colourless
• oxidation state of manganese changes from +7 to +2

Question 20

potassium iodide

Answer 20

KI reducing agent
I- ions oxidised to iodine molecules, I2

• colourless to brown
• oxidation state of iodine changes from -1 to 0

Question 21

oxidation and reduction

Answer 21

OILRIG
o - loss of e, gain of oxygen
r - gain of e, loss of oxygen

Question 22

equilibrium

Answer 22

when forward and backward reaction in a reversible reaction are going at exactly same rate.

Question 23

le Chatelier’s principle

Answer 23

when a change is made to conditions of a system at equilibrium, system automatically moves to oppose the change.

Question 24

higher temperature =

Answer 24

equilibrium moves in endothermic direction

Question 25

higher pressure

Answer 25

equilibrium moves in direction that produces the smallest amount of molecules of gas.

Question 26

higher concentration

Answer 26

to favour opposite

Question 27

recycling definition

Answer 27

process of converting waste materials into new products

Question 28

+ and - to metal recycling

Answer 28

+: less energy (cheaper), conserves finite amount of each metal, saves costs of mining and extracting, less waste sent to landfill
-: sorted and separated = time and money
energy to collect, transport, recycle (still less)