5.2 - Energetics

Question 1

What is the enthalpy change of a reaction?

Answer 1

heat energy lost or absorbed per mole

Question 2

What is the symbol for enthalpy change?

Answer 2

ΔH

Question 3

A positive enthalpy change is…

Answer 3

endothermic

Question 4

A negative enthalpy change is…

Answer 4

exothermic

Question 5

What are the units for enthalpy change?

Answer 5

kJ/ mol

Question 6

How can enthalpy changes be represented?

Answer 6

on an energy level diagram

Question 7

In an exothermic reaction, the products end up with…

Answer 7

less energy than the reactants (as heat energy is released)

Question 8

What 2 factors contribute to a reaction’s enthalpy change?

Answer 8

-breaking bonds
-making bonds

Question 9

When bonds are broken, heat energy is…

Answer 9

absorbed (endothermic)

Question 10

When bonds are made, heat energy is…

Answer 10

released (exothermic)

Question 11

The amount of heat energy each bond absorbs or releases is called…

Answer 11

bond energy (BE)

Question 12

How can you calculate enthalpy change using bond energies?

Answer 12

bonds broken - bonds made

Question 13

The energy required to break the bonds is called…

Answer 13

activation energy

Question 14

What is calorimetry?

Answer 14

experimental method to measure an enthalpy change

Question 15

Measuring enthalpy change: exothermic

Answer 15

-releases heat energy
-heat energy is absorbed by nearby water
-temperature of water increases

Question 16

Symbol equation for heat energy (Q) of an experiment

Answer 16

Q = mcΔT

Question 17

Word equation for heat energy (Q) of an experiment

Answer 17

heat energy = mass of water x temperature change x specific heat capacity (of water)

Question 18

What is the specific heat capacity of water?

Answer 18

4.18 J/g/C

Question 19

Symbol equation for enthalpy change (ΔH) of an experiment

Answer 19

ΔH = −Q ÷ moles

Question 20

Word equation for enthalpy change (ΔH) of an experiment

Answer 20

enthalpy change = (minus) heat energy ÷ moles reacted