Chemistry Chapter 17 – Davidson
What are the ways in which energy change can occur?
Energy changes occur as either heat transfer or work, or a combination of both
What happens to the energy of the universe during a chemical or physical process?
During any chemical or physical process, the energy of the universe remains unchanged
On what factors does the heat capacity of an object depend?
The heat capacity of an object depends on both its mass and its chemical composition
thermochemistry
the study of energy that can occur during chemical reactions and changes in state
chemical potential energy
energy stored in chemical bonds
heat
energy that transfers from one object to another because of a temperature difference between the objects
system
a part of the universe on which you focus your attention
surroundings
everything in the universe outside of the system
law of conservation of energy
in any chemical or physical process, energy is neither created nor destroyed
endothermic process
a process that absorbs heat from the surroundings
exothermic process
a process that releases heat to its surroundings
heat capacity
the amount of heat needed to increase the temperature of an object exactly 1°C
specific heat
the amount of heat needed to increase the temperature of 1g of a substance 1°C; also called specific heat capacity
How can you measure the change in enthalpy of a reaction?
The value of ∆H of a reaction can be determined by measuring the heat flow of the reaction at constant pressure
How can you express the enthalpy change for a reaction in a chemical equation?
In a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product
calorimetry
the precise measurement of heat flow out of a system for chemical and physical processes
calorimeter
an insulated device used to measure the absorption or release of heat in chemical or physical processes
enthalpy
the heat content of a system at constant pressure
thermochemical equation
a chemical equation that includes the enthalpy change
heat of reaction
the enthalpy change for a chemical equation exactly as it is written
heat of combustion
the heat of reaction for the complete burning of one mole of a substance
What is the relationship between molar heat of fusion and molar heat of solidification?
The quantity of heat absorbed by a melting solid is exactly the same as the quantity of heat released when the liquid solidifies; that is ∆H(fus) = -∆H(solid)
What is the relationship between molar heat of vaporization and molar heat of condensation?
The quantity of heat absorbed by a vaporizing liquid is exactly the same as the quantity of heat released when the vapor condenses; that is, ∆H(vap) = -∆H(cond)
What thermochemical changes can occur when a solution forms?
During the formation of a solution, heat is either released or absorbed
molar heat of fusion
the amount of heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature
molar heat of solidification
the amount of heat lost by one mole of a liquid as it solidifies at a constant temperature
molar heat of vaporization
the amount of heat absorbed by one mole of a liquid as it vaporizes at a constant temperature
molar heat of condensation
the amount of heat released by one mole of a vapor as it condenses to a liquid at a constant temperature
molar heat of solution
the enthalpy change caused by the dissolution of one mole of a substance
How can you calculate the heat of reaction when it cannot be directly measured?
Hess’s law allows you to determine the heat of reaction indirectly by using the known heats of reaction of two or more thermochemical equations
Hess’s law of heat summation
if you add two or more thermochemical equations to give a final equation, then you also add the heats of reaction to give the final heat of reaction
standard heat of formation
the change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states at 25°C