enthalpy changes

Question 1

law of conservation of energy

Answer 1

energy can’t be created or destroyed

Question 2

what’s an exothermic reaction

Answer 2

exothermic reaction releases energy to surroundings, so they get hotter

Question 3

what’s an endothermic reaction

Answer 3

endothermic reactions absorb energy from the surroundings so it gets colder

Question 4

is breaking bonds endo or exo

Answer 4

endo

Question 5

is making bonds endo or exo

Answer 5

exo

Question 6

phrase to remember this

Answer 6

bendo mexo

Question 7

enthalpy change equation

Answer 7

change in products - change in reactants

Question 8

is exothermic enthalpy positive or negative

Answer 8

negative
because system loses energy to surroundings

Question 9

is endothermic enthalpy positive or negative

Answer 9

positive
energy taken into system

Question 10

describe energy profile of exothermic reaction

Answer 10

starts high (reactants) ends low (products)
activation energy from reactants to peak
enthalpy change from reactants to products

Question 12

describe endothermic reactant profile

Answer 12

starts low (reactants) ends high (products)
activation energy from reactants to peak
enthalpy change is from reactants to products

Question 13

examples of an exothermic reaction

Answer 13

combustion
vapour condensation
fire
hand warmer
acid neutralisation

Question 14

examples of endothermic reactions

Answer 14

photosynthesis
thermal decomposition
chemical ice pack
liquid vaporising
melting ice

Question 15

thermal decomposition equation

Answer 15

metal carbonate - - metal oxide + carbon dioxide

Question 16

combustion equation

Answer 16

fuel + oxygen - - - carbon dioxide + water
oxygen can be half numbers

Question 17

what’s average bond enthalpy

Answer 17

bonds broke - bonds made
endo - exo
reactants - products usually

Question 18

how to work it out in a question

Answer 18

use the values to calculate all the bonds in table for reactants then products then take them away from eachother

Question 19

if more energy is released than absorbed it’s

Answer 19

exothermic

Question 20

if more energy is absorbed than released its

Answer 20

endothermic