unit 9 thermochemistry Flashcards
calorimeter
device used to measure heat absorbed or released
calorie
quantity of heat needed to raise the temperature of 1g of water by 1 degrees Celsius
Joule
SI unit of energy
enthalpy
heat content of a system at constant pressure
specific heat
quantity of heat needed to raise the temperature of 1g of a substance by 1 degrees Celsius
heat capacity
quantity of heat needed to raise the temperature of an object by 1 degrees Celsius
molar heat of fusion
amount of heat needed to melt one mole of a solid at constant temperature
sublimation
process by which a solid changes directly to a gas
exothermic reaction
releases heat energy
example of exothermic reactions:
combustion, rain, freezing
what side is the heat energy (delta H) on in an exothermic reaction?
the right side/product side
what is enthalpy?
The heat energy change (delta H) that takes place when reactants go to products.
what does a positive enthalpy mean?
heat is absorbed during the reaction, endothermic reaction
what does a negative enthalpy mean?
heat is released during the reaction, exothermic reaction
endothermic reaction
absorbs heat energy
examples of endothermic reactions:
photosynthesis, cooking, melting
what side is the heat energy on in an endothermic reaction?
the reactants side
Define the law of conservation of energy
energy is conserved and never created nor destroyed
What principle advocates for equilbrium?
Le Chatlier’s Principle
61.2 kJ + 2 [A] –> [B]
If we add more of A, which way does it shift and what increases in concentration?
If we add more of A, the energy would shift to the products side and B’s concentration would increase
61.2 kJ+ 2 [A] –> [B]
If we decrease the pressure, what way does it shift?
To [A], because the shift in Pressure is based on moles, and A needs to have more moles
61.2 kJ+ 2 [A] –> [B]
If we increase the temperature, what substance increases?
[B], because the kJ is on the reactants side and it needs to shift to products side
During phase changes, what happens to the temperature?
Stays constant
What happens to the energy when breaking bonds?
Energy supplied/absorbed
What happens to the energy when forming bonds?
Energy released
What is chemical potential energy?
The energy stored in the chemical bonds of a substance.
Where is the temperature changing in a heating curve?
The diagonal lines: /
What do heating curves show?
Shows how a substance’s temperature changes as heat is added and displaying phase changes
what’s the symbol for enthalpy?
delta H
How do you calculate the heat energy absorbed in a phase change in a heating curve?
q= n (moles) times enthalpy of fusion (delta H fus)
Where are the phases changing in a heating curve?
The flat lines : —
The 1st flat line is equal to ? :
The enthalpy of fusion
The 2nd flat line is equal to ? :
The enthalpy of vaporization
How do you calculate the heat energy absorbed in a phase change (ex: ice going to liquid water) from a heating curve?
Divide the enthalpy of vaporization by the enthalpy of fusion.
Kinetic Energy and temperature’s relationship?:
Direct
What happens in segments 1,3, and 5?
The kinetic energy is increasing
What happens in segments 2 and 4 in relation to energy?
The potential energy is increasing
How do you calculate the heat energy absorbed in segments 1,3, and 5?
Use q=mCdeltaT
What’s a phase diagram show?
The different states of matter and when they transition according to temperature and pressure
What is entropy?
A measure of the disorder of a system
Example of entropy
A campfire
How do you calculate the enthalpy change from products and reactants?
Sum of enthalpies of the product-sum of enthalpies of the reactants
or use q=mCdeltaT
Definition of boiling
the process by which a liquid turns into a vapor when it is heated to its boiling point
Definition of evaporation
Liquid->Gas NOT at boiling point at the surface of a liquid
Definition of vaporization
Liquid->Gas AT boiling point
More temp. and pressure required to break bonds=?
Stronger bonds
Sublimation
solid->gas
condensation
gas->liquid
deposition
gas->solid
when to use delta H fusion formula?
when there is a phase change
when to use delta H vaporization formula?
Vaporize substance (liquid->gas)
A higher temperature with the same volume=
Higher entropy
What 4 factors affect reaction rate?
Presence of a catalyst, concentration, temperature, surface area
What happens when you add a catalyst to a reaction?
Speeds up the reaction rate and it increases the activation energy
What happens when you increase the temperature in a reaction?
The reaction rate increases as the number of effective collisions increases.
Which combination of positive/negative delta S and delta H favors a spontaneous reaction?
Positive delta S, negative delta H
thermochemistry
the study of the transfers of energy as heat that accompany chemical reactions and physicals changes
what is an activated complex
a transitional structure that results from an effective collision that persists while old bonds are breaking and new bonds are forming
