Energetics

Question 1

what is enthalpy change?

Answer 1

the heat transferred in a reaction at constant pressure

Question 2

what are standard conditions?

Answer 2

100kpa

298k

Question 3

what is an exothermic reaction?

Answer 3

energy is given out to the surroundings so the temperature goes up,and products have less energy than reactants

Question 4

what is an endothermic reaction?

Answer 4

takes in energy from the surroundings ,temp falls, the products have more energy than reactants.

Question 5

what is the standard enthalpy of combustion?

Answer 5

the enthalpy change when 1 mole of substance is completely burned in oxygen under standard conditions with all reactants and products in their standards states

Question 6

what is the standard enthalpy of formation?

Answer 6

the enthalpy change when 1 mole of compound is formed from its constituent elements in their standard states under standard conditions.

Question 7

what is mean bond enthalpy?

Answer 7

the average enthalpy need to break different types of molecules

Question 8

how do you calculate the enthalpy change of a reaction?

Answer 8

bonds broken-bonds formed

Question 9

why do mean bond enthalpy calculations differ from hess law?

Answer 9

(MBE) only uses averages which is less accurate

Question 10

what charge is an exothermic reaction

Answer 10

-

Question 11

what charge is an endothermic reaction

Answer 11

+

Question 12

why is the standard formation of barium and aluminum 0

Answer 12

they are elements

Question 13

what are problems with the calorimetry

Answer 13

• heat is absorbed by container

- heat is lost to surroundings

Question 14

what are problems with the flame calorimeter

Answer 14

• combustion may be incomplete

- some flammable liquid may escape by evapouration

Question 15

what is the difference between heat and temperature

Answer 15

heat is a measure of total energy while temp is the average Ke

Question 16

state hess’ law

Answer 16

the total enthalpy change for a reaction is independent of the route taken

Question 17

how do you calculate enthalpy change of formation with hess law

Answer 17

-write under the reation list of all the elemts involved
-label the arrows pointing up
–>
\ /
-use formula AH^1=AH^2+AH^3

Question 18

how do you workout the enthalpy change of combustion with hess law

Answer 18

arrows point towards combustion products

-

Question 19

what does q=mcAT mean

Answer 19

q=heat loss/gained
m=mass(g)
c=specific heat capacity
AT=change in temperature(k)

Question 20

what is the units for hess’ law

Answer 20

kjmol-1

Question 21

how do u calculate the standard enthalp of combustion using the actual heat change in reaction

Answer 21

q/no. of moles

Question 22

what is a flame calorimeter used for

Answer 22

measure the heat energy produced in a combustion reaction