reactivity 1.2

Question 1

define chemical bond

Answer 1

a force of attraction between two atoms

Question 2

breaking bonds are what type of process?

Answer 2

endothermic because breaking the bond requires the input of energy

Question 3

when bonds are broken or made, ______ changes take place

Answer 3

enthalpy

Question 4

what does the energy change required to break the bond depend on?

Answer 4

the atoms that form the bond

Question 5

define bond dissociation enthalpy

Answer 5

the energy required to break a particular bond

Question 6

other terms for bond dissociation enthalpy x2

Answer 6

bond enthalpy OR bond energy

Question 7

bond formation is an _______ process

Answer 7

exothermic

Question 8

if more energy is released when new bonds are formed than energy is required to break bonds, the reaction is ________. which is more stable (products v reactants)?

Answer 8

exothermic, products are more stable than reactants

Question 9

if more energy is required to break bonds than energy is released when new bonds are formed, the reaction is ________. which is more stable (products v reactants)?

Answer 9

endothermic, products are less stable than reactants

Question 10

bond energies are affected by ____ ____ in the molecule (the environment)

Answer 10

other atoms

Question 11

define average bond energy

Answer 11

the energy needed to break one mole of bonds in a gaseous molecule averaged over similar compounds

Question 12

how to find the average bond enthalpy for C-H

Answer 12

take the bond dissociation enthalpy for the whole molecule and divide it by the number of C-H bonds

Question 13

how to find standard enthalpy of reaction when experimentation is not an option? equation?

Answer 13

by using bond energies
ΔH^ꝋᵣ = ΔH for bonds broken + ΔH for bonds formed

Question 14

define hess’s law

Answer 14

the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same (whether the reaction takes place in one or two steps, the total enthalpy change of the reaction will still be the same)

Question 15

the enthalpy change from _____ to _____ (direct route) is equal to the enthalpy change of _____ forming ____ and then ___ (indirect route)

Answer 15

elements to products, elements forming reactants and then products

Question 16

what is ΔH₂ (hess’s law energy cycles)

Answer 16

the products can be directly formed from the elements

Question 17

what is ΔH₁ and ΔHᵣ (hess’s law energy cycles)

Answer 17

the products can be indirectly formed from the elements

Question 18

equation for direct route between elements → products (hess’s law energy cycles)

Answer 18

ΔH₂ = ΔH₁ + ΔHᵣ

Question 19

when is hess’s law used?

Answer 19

to calculate enthalpy changes which can’t be found experimentally using calorimetry

Question 20

two methods to solve hess’s law problems

Answer 20

using cycles AND using equations

Question 21

what can hess’s law be used to calculate?

Answer 21

the standard enthalpy change of a reaction from known standard enthalpy changes

Question 22

two key rules for hess’s law

Answer 22

if you follow the direction of the arrow you add the quantity AND if you go against the arrow you subtract the quantity