DF1/DF2 (Enthalpy Changes & Hesse’s law)

Question 1

is bond breaking endothermic?

Answer 1

yes

Question 2

what is bond making?

Answer 2

exothermic

Question 3

what is the enthalpy change for an exothermic and endothermic reaction?

Answer 3

exo is negative, endo is positive

Question 4

what is the equation for enthalpy change?

Answer 4

energy of the products - energy of the reactants

Question 5

why is delta H negative for exothermic reactions?

Answer 5

because energy has been lost from the chemical bonds to the surroundings

Question 6

what are the 3 standard conditions for enthalpy?

Answer 6

standard temperature 298K
100kPa
1M concentration

Question 7

how do you convert kelvin to celsius and vice versa?

Answer 7

celsius to kelvin, add 273
kelvin to celsius, minus 273

Question 8

what is the standard enthalpy change for a reaction?

Answer 8

the enthalpy change when molar quantities of reactants react together under standard conditions

Question 9

what is the standard enthalpy change of combustion?

Answer 9

when one mole of a substance is burnt completely in oxygen

Question 10

what is the standard enthalpy change for formation?

Answer 10

enthalpy change that occurs when one mole of a compound is formed from its elements

Question 11

what is standard enthalpy change of neutralisation?

Answer 11

enthalpy change that can be measured from the energy given out when acids react with alkalis in aqueous solutions.

Question 12

how do you use Hesse’s law to draw enthalpy cycles?

Answer 12

write the equation you’re trying to find at the top of the cycle
look at the given data
look at the third elements/compounds in the triangle
make the triangle
work out how to calculate deltaH1
add the values