Thermochemistry

Question 1

What is ENERGY?

Answer 1

The ability to do work

Energy is not matter, but a property of matter.

Question 2

What are the units for energy?

Answer 2

Joules (J)

Common conversions: 1 kJ = 10^3 J, 1 MJ = 10^6 J, 1 GJ = 10^9 J.

Question 3

What are the two parts to consider in thermochemistry?

Answer 3

SYSTEM & SURROUNDINGS

The system is where the reaction is happening, while the surroundings encompass everything else in the universe.

Question 4

Define an Isolated system.

Answer 4

No exchange of matter or energy

It is impossible to have a perfect isolated system.

Question 5

Define a Closed system.

Answer 5

Exchange of energy, not matter

An example is a container with a lid.

Question 6

Define an Open system.

Answer 6

Exchange of both matter and energy

An example is a beaker.

Question 7

What does the law of conservation of energy state?

Answer 7

Energy cannot be created or destroyed; only converted from one form to another

Energy lost equals energy gained.

Question 8

Is any energy conversion 100% efficient?

Answer 8

No

All energy conversions have some inefficiency.

Question 9

What is Kinetic Energy represented as?

Answer 9

Ek

Average Ek is the temperature. Also known as heat transfer between objects

Question 10

What does Heat (Q) refer to?

Answer 10

The transfer of thermal (kinetic) energy between objects

Example: A cup of coffee cooling down transfers energy into the air.

Question 11

Fill in the blank: The system plus the surroundings equals the _______.

Answer 11

universe

Question 12

What is the goal of predicting energy changes in chemical processes?

Answer 12

To predict the direction and extent of change itself.

Question 13

What is the System

Answer 13

Where the reaction is happening
ex. reactants, products, and solvents)

Question 14

Temperatures in relation to Ek, kinetic energy
High Temp=
Low temp =

Answer 14

High temp= more Ek
Low temp= less Ek

Question 15

What happens to metal when it is heated?

Answer 15

Metal absorbs heat.

This is measured in joules.

Question 16

What are the types of energy (Ek)?

Answer 16

1.) Vibrational (all forms of matter)
2.) Rotational (liquids and gases - NO solids)
3.) Translational (gases only)

Particles move at random, in straight lines/tangents.

Question 17

What is Potential Energy (Ep)?

Answer 17

Ep is bond energy, stored in the bonds of a substance’s molecules , chemical bonds are broken and formed in chemical reactions

Question 18

What happens to energy when chemical bonds are broken?

Answer 18

Energy is absorbed from the surroundings when bonds are broken bc it requires energy to break it apart making it endothermic

Question 19

What happens to energy when chemical bonds are formed?

Answer 19

Energy is released , typically as heat bc it’s excessive, this makes it a exothermic process

Question 20

Which process is endothermic?

Answer 20

Breaking bonds is an endothermic process, energy is absorbed FROM the surroundings

Question 21

What process is exothermic

Answer 21

Forming bonds which releases energy

Question 22

What are Intermolecular Bonds IMFs
>types

Answer 22

Bonds between molecules
These bonds are formed and broken during a phase change
Weakest type of bonds
Hydrogen bonds, LDFs, (all have), dipole-dipole

Ex Between two Water molecules

Question 23

Which is endothermic and exothermic order in phase change in IMFs

Answer 23

Solid>Liquid>Gas (IMFs broken, endothermic)

Gas>Liquid>Solid (IMFs formed, exothermic)

Question 24

What are IntRAmolecular forces?
> order of strength

Answer 24

Chemical bonds within molecules between individual atoms/ions (so between H and O in H2O)
Covalent or Ionic
Energy changes occur when these types of bonds are made or broken during chem reactions
> Network then Ionic then Covalent top 3 strongest bonds

Question 25

Nuclear bonds

Answer 25

Bonds eithin nucleus , between protons and neutrons strongest type of bond

Question 26

What is the order of bonds strength

Answer 26

Intranuclear > (Intramolecular) Ionic> Metallic > (Intramolecular) covalent > IMFs

Question 27

Potential energy change results from

Answer 27

a rearrangement of bonds

Question 28

A kinetic energy change results from

Answer 28

a change in molecular motion, how fast or slow particles r moving in molecules

Question 29

What is a combustion reaction

Answer 29

A substance reacts with oxygen gas and produces carbon dioxide and water vapours (gases) exo

Question 30

Calculating Ek is for __ and __ > Formula and variables

Answer 30

water and containers > Q= mc🔺T Q- quantity of thermal E released or gained by substance as heat (J or kJ) m- mass (g or kg) c- specific heat capacity pg.3 data book 🔺T- change in temp Tfinal - Tinitial

Question 31

What is specific heat capacity? > low and its corilation w energy > high and its correlation w energy

Answer 31

c= the amnt of energy required to heat 1h of substance by 1C (have to change to be 1g) > low c (metals) require less input energy to increase energy (ex. pans heat up fast) > high c (water) require more energy to increase temp (take longer to heat up n cool down)

Question 32

%diffrence formula

Answer 32

|(actual - theoretical )/ theoretical |

Question 33

Where does all our energy come from

Answer 33

The sun

Question 34

Whats calorimetry

Answer 34

method of condensing the universe into a limited space and measuring changes in state and heat transfer inside calorimeter

Question 35

When doing calolimetry what are the lab equipment and how do u measure the heat transfer

Answer 35

System= inside container where reaction is happening Surroundings = water in inside Calorimeter- insulated container The change in temp measured w a thermometer = Q=mc🔺T to find heat transfer Q = same as change in energy

Question 36

What type of energy is involved in a chem reaction and phase change? therefore?

Answer 36

Ep > chem change= bonds breaking and forming > phase= IMFs break of form therefore the heat transfer is the same as the change in energy 🔺T=🔺Ek

Question 37

What is Enthalpy(H)

Answer 37

The total Ek and Ep of a system > however cant measure Ep only Ek in kJ > internal energy

Question 38

Whats Enthalpy of Reaction (🔺H) > formula

Answer 38

the change in enthalpy between the products and the reactants in kJ > can be pos or neg depending on wether energy is absorbed or released 🔺 is final - initial > 🔺H= Hprod-Hreactants

Question 39

When is Enthalpy of reaction pos and neg

Answer 39

Positive when endothermic so when it absorbs and the number is on reactant side Neg when exothermic so when it releases and number is on products side

Question 40

What is changing in the calorimetry system What is the cause of change So

Answer 40

temperature Ep change So 🔺H= 🔺Ep = Q

Question 41

Types of Ek and what they are

Answer 41

Vibrational: all forms of matter Rotational: liquids and gasses Translational: only gasses random straight line movement

Question 42

Combistion results from changes in ___ energy resulting from ___

Answer 42

Potential A rearrangement of bonds

Question 43

In questions Ek is the ___ while Ep is ___

Answer 43

Ek- overall avrage of heat transffere (whjjolecthibg whhole avrg) Ep- bond energy either endo or exo bc its ehats changing

Question 44

Cellular Respiratio is what kind of reaction

Answer 44

exothetmic bc releases energy

Question 45

Photosynthesis iscehat kind of rxn And Formation of glucose is what kind of rxn

Answer 45

endothetmic reaction when in form of water + oxygen exothetmic bc from elements bc formation look in databook

Question 46

All combustion rxns are

Answer 46

exothetmic

Question 47

Whhat is heat, temp, thermal energy

Answer 47

heat- transfer if kinetic energy Temp- avrg kinetic energy of particles Thermal - sum of ek n ep

Question 48

Teo samples at 50celsius does the 100g or 500g sample have more thermal energy - sum which has more thermal energy

Answer 48

The bigger sample because same temp Ek but bigger one takes more energy to heat it up

Question 49

Endothermic reaction energy is ___ usually ___ 🔺H is Exothermic reaction enetgy is __ usually ___ 🔺H id

Answer 49

abosrbed non spont positive releaseed spont negative

Question 50

Heat refers to the

Answer 50

transfer of Thermal (Ek) energy between objects

Question 51

What’s a combustion reaction

Answer 51

any rxn where a material reacts with j O2 and produces CO2 and H2O is exothermic

Question 52

The formation rxn of something is found ___ so decomp rxn is ___

Answer 52

in data booklet opposite sign

Question 53

Molar enthalpy and enthalpy r both represented by ___ but

Answer 53

🔺H Molar is in Kj or J / mol and enthalpy is just Kj