thermochemistry 1 ( lesson 1-3, lesson 1 is breif)

Question 1

What is the basic definition for thermochemistry?

Answer 1

The study of heat changes that occur during chemical reactions. It is interested in the flow of heat from the system to the surroundings or vice versa

Question 2

System meaning

Answer 2

the tiny bit of the universe you are interested in
- Open: both energy and matter can enter/leave
- closed: energy can enter/leave but matter cannot
- isolated: neither energy nor matter can enter or leave the system

Question 3

Surroundings meaning

Answer 3

everything else in the universe

Question 4

what is energy?

Answer 4

The capacity for doing work or supplying heat

Question 5

what are the two fundamental types of energy?

Answer 5

Kinetic energy (Ek) - the energy of motion (of particles)
Potential energy (Ep) - energy that is stored in chemical bonds

Question 6

Heat meaning?

Answer 6

Heat: Transfer of thermal energy from one system to another

Question 7

What is the first law of thermodynamics?

Answer 7

the total energy of the universe is constant

Energy can be converted to other forms, however, the total energy of any system is conserved (it cannot be created or destroyed)

Question 8

What is the second law of thermodynamics?

Answer 8

In the absence of energy input, a system becomes more disordered

Heat will always transfer from hot objects to coolers objects until thermal equilibrium is reached

Question 9

What is energy is the temperature a measure of?

Answer 9

temperature is a measure of the average kinetic energy of the particles of a substance

The faster the particles are moving, the higher the temperature

Question 10

What is the definition of heat capacity?

Answer 10

Heat capacity is heat required to change the temperature of one gram of a substance by 1 °C

Question 11

What is the definition of enthalpy?

Answer 11

enthalpy is the sum of all forms of kinetic and potential energy in a system (Ek + Ep)

Question 12

What is ∆ᵣH measured in?

Answer 12

J or KJ

Question 13

What does the “°” mean in ∆ᵣH°

Answer 13

it means it happens at SATP (100 kPa and 25°C)

Question 14

What happens in an endothermic reaction?

Answer 14

the energy added to break bonds is greater than the energy released when the new bonds are formed.
Endothermic changes are designated as positive values since energy is being added to the system

Question 15

What happens in an exothermic reaction?

Answer 15

the energy added to break the bond is less than the energy released when new bonds are formed

exothermic changes are designated as negative values since energy is being removed from the system

Question 16

What happens in a photosynthesis reaction?

Answer 16

Photosynthesis produces glucose (C₆H₁₂O₆) and oxygen (O₂) from carbon dioxide and water

Cellular respiration does the opposite (products and reactants swap places)

(photosynthesis is endothermic, cellular respiration is exothermic)

Question 17

In exothermic reactions, what is the first way of expressing enthalpy change?

Answer 17

1. ∆ᵣH Notation
   the heat of the reaction can be given as a ∆ᵣH value outside of the equation
   the ∆ᵣH sign is negative since the enthalpy of the system is decreasing

Question 18

In exothermic reactions, what is the second way of expressing enthalpy change?

Answer 18

2. ∆ᵣHₘ notation
   Molar enthalpy of reaction for 1 mol of a substance
   the heat of reaction can be given as a ∆ᵣHₘ value outside of the equation
   divide ∆ᵣH by amount of moles substance reported

Question 19

In exothermic reactions, what is the third way of expressing enthalpy change?

Answer 19

3. Inside the equation
   In an exothermic, enthalpy is included as a product (add enthalpy to other product)

Question 20

what do potential energy diagrams show and what do you need to label?

Answer 20

• Shows the potential energy of the reactants and the products of a chemical reaction
• Reactants have more potential energy than the products in an exothermic reaction (energy has been lost to the surroundings)
• Reactants have less potential energy than the products in an exothermic reaction (energy has been gained by the system)
• The difference between the reactants and the products is the ∆ᵣH
• label “reaction progress” on the x axis. Ep (KJ or J) on the y axis, give it a title, and include difference (∆ᵣH) between the reactant and products line.

Question 21

In endothermic reactions, what is the first way of expressing enthalpy change?

Answer 21

1. ∆ᵣH Notation
   the sign on ∆ᵣH is positive since the enthalpy of the system is increasing

Question 22

In endothermic reactions, what is the second way of expressing enthalpy change?

Answer 22

2. ∆ᵣHₘ Notation
   molar enthalpy of reaction for 1mol of a substance
   divide ∆ᵣH by the amount of moles substance reported

Question 23

In endothermic reactions, what is the third way of expressing enthalpy change?

Answer 23

3. Inside the equation
   In an endothermic reaction enthalpy is included as a reactant (add to other
   reactant)

Question 24

What is calorimetry?

Answer 24

The technological process of measuring energy changes using an isolated system

Question 25

What is a calorimeter?

Answer 25

the isolated system used to determine the heat involved in a phase change or in a chemical reaction.

Question 26

what are the main points of a simple calorimeter?

Answer 26

• styrofoam is neglected in calculations
• Do not use mass of reactant in equation
  - However, if it is a solution, the mass of the water is important
  - 1mL of water = 1g

Question 27

How are calculations based on the principle of Heat Transfer?

Answer 27

HEAT/ENERGY LOST = HEAT/ENERGY GAINED

remember you must use a sign with your ∆H values (either enthalpy change or molar enthalpy
endothermic = positive value
exothermic = negative value

Question 28

What are industrial bomb calorimeters?

Answer 28

• they are calorimeters that are used in research to measure the heat of combustion of food, fuel, oil, crops and explosives
• Modern calorimeters have fixed componenets -volume of water used, container (bomb), material, stirrer, thermometer-

Question 29

How to calculate the energy of combustion for a bomb calorimeter?

Answer 29

In calculating the energy of combustion, you take all components of the calorimeter into account: Eₜₒₜₐₗ = mcΔt (H₂O) + mcΔt (stirrer) + mcΔt (bomb) + mcΔt (thermometer)

Usually, however, all of the “mc” parts are constant so they can be replaced by one constant C which is the total heat capacity of the entire system in KJ/C. GIving the formula CΔT