thermochemistry 1 ( lesson 1-3, lesson 1 is breif) Flashcards
What is the basic definition for thermochemistry?
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
System meaning
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
Surroundings meaning
everything else in the universe
what is energy?
The capacity for doing work or supplying heat
what are the two fundamental types of energy?
Kinetic energy (Ek) - the energy of motion (of particles)
Potential energy (Ep) - energy that is stored in chemical bonds
Heat meaning?
Heat: Transfer of thermal energy from one system to another
What is the first law of thermodynamics?
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)
What is the second law of thermodynamics?
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
What is energy is the temperature a measure of?
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
What is the definition of heat capacity?
Heat capacity is heat required to change the temperature of one gram of a substance by 1 °C
What is the definition of enthalpy?
enthalpy is the sum of all forms of kinetic and potential energy in a system (Ek + Ep)
What is ∆ᵣH measured in?
J or KJ
What does the “°” mean in ∆ᵣH°
it means it happens at SATP (100 kPa and 25°C)
What happens in an endothermic reaction?
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
What happens in an exothermic reaction?
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
What happens in a photosynthesis reaction?
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)
In exothermic reactions, what is the first way of expressing enthalpy change?
- ∆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
In exothermic reactions, what is the second way of expressing enthalpy change?
- ∆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
In exothermic reactions, what is the third way of expressing enthalpy change?
- Inside the equation
In an exothermic, enthalpy is included as a product (add enthalpy to other product)
what do potential energy diagrams show and what do you need to label?
- 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.
In endothermic reactions, what is the first way of expressing enthalpy change?
- ∆ᵣH Notation
the sign on ∆ᵣH is positive since the enthalpy of the system is increasing
In endothermic reactions, what is the second way of expressing enthalpy change?
- ∆ᵣHₘ Notation
molar enthalpy of reaction for 1mol of a substance
divide ∆ᵣH by the amount of moles substance reported
In endothermic reactions, what is the third way of expressing enthalpy change?
- Inside the equation
In an endothermic reaction enthalpy is included as a reactant (add to other
reactant)
What is calorimetry?
The technological process of measuring energy changes using an isolated system
