energetics

Question 1

endothermic

Answer 1

positive enthalpy change, energy taken in from the surroundings

Question 2

exothermic

Answer 2

negative enthalpy change, energy is released

Question 3

enthalpy change definition

Answer 3

the heat energy change measured under conditions of constant pressure

Question 4

standard enthaply change refers to

Answer 4

standard conditions
100kPa
298K

Question 5

define enthalpy of formation

Answer 5

the enthalpy change when one mole of a substance is produced from its elements under standard conditions

Question 6

define enthalpy of combustion

Answer 6

the enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions

Question 7

heat change eqaution

Answer 7

q=mc¬t
m is mass of substance that has a temp change
¬t is change in temp
c is specific heat capacity

Question 8

molar enthalpy change equation

Answer 8

¬h = q/n

Question 9

experimental method for finding enthalpy change

Answer 9

measuring temp change over time plot on graph temp vs time, extrapolate back to when chemicals mixed to give accurate value for change in temp

Question 10

define hess’s law

Answer 10

energy in a reaction must be conserved, as it cannot be created or destroyed. therefore the overall enthalpy change for a reaction is the same regardless of the route taken

Question 11

overall enthalpy change =

Answer 11

sum of bonds broken - sum of bonds formed

Question 12

define mean bond enthalpy

Answer 12

the energy required to break one mole of stated bond in gaseous state, under standard conditions averaged over a range of different compounds

Question 13

why do values from mean bond enthalpy calculations differ from those determined using hess law

Answer 13

its a value averaged over a range of compounds not that specific compound