8: pre/post questions
= H products - H reactants
change in enthalpy
=final temperature- initial temperature
change in temperature
The unit of measure for change in the enthalpy according to the International System of Units
joule
When a reaction is exothermic, the enthalpy of the products is _____ the reactants. greater than less than equal to
less than
= moles of solute (mol)/ volume of solution (l)
molarity
experimental value - theoretical value ------------------------------------------ x 100% (theoretical value)
percent error
The change in enthalpy of a reaction is equal to the enthalpy of the _____ minus the enthalpy of the _____. products; reactants reactants; products None of the above
products; reactants
The study of heat that accompanies chemical reactions
thermochemistry
Calculate the percent error of a chemical reaction with a theoretical value of -45.68 kJ/mol and an experimental value of -54.78 kJ/mol. 20.10% 16.61% 19.92% 21.37%
19.92%
Reaction that absorbs heat from the surrounding environment
endothermic
When an _____ reaction occurs the products have a greater enthalpy than the reactants, whereas during an ____ reaction the enthalpy of the products is less than the enthalpy of the reactants. exothermic; endothermic endothermic; exothermic
endothermic; exothermic
The internal energy of a system that includes heat plus the product of pressure and volume
enthalpy
A chemical reaction that releases heat to the surrounding environment is considered _____. endothermic exothermic
exothermic
Reaction that releases heat to the surrounding environment
exothermic
When an _____ reaction occurs in an aqueous solution, heat will be released to the water. endothermic exothermic
exothermic
Categorize each statement as representing an exothermic or endothermic reaction. -temperature increases -temperature decreases -heat is released to surroundings -heat is absorbed from surroundings -the change in enthalpy is a negative number -the change in enthalpy is a positive number
exothermic: -temperature increases -heat is released to surroundings -the change in enthalpy is a negative number endothermic: -temperature decreases -heat is absorbed from surroundings -the change in enthalpy is a positive number
The change in enthalpy of a reaction is equal to the enthalpy of the reactants minus the enthalpy of the products. true or false
false
Enthalpy is the external energy of the system, E, which includes heat plus the product of pressure and volume. true or false
false; internal energy
= (mass of solution) x (specific heat) deltaT
heat gain or loss
In an endothermic reaction _____. -heat is released and temperature increases -heat is released and temperature decreases -heat is absorbed and temperature decreases -heat is absorbed and temperature increases
heat is absorbed and temperature decreases
States the total change in enthalpy is independent of the pathway
hess's law
The amount of heat given off or absorbed by a chemical reaction is called _____. an exothermic reaction the change in enthalpy a Joule the product of pressure and volume
the change in enthalpy
Hess's Law indicates that if a reaction takes place in one or multiple steps, the change in enthalpy for the overall process must be the sum of the change in enthalpy of the constituent reactions. true or false
true
Hess's law states that the total change in enthalpy is independent of the pathway true or false
true
If an experiment has a qrxn of 518.07 J, calculate the change in enthalpy of the reaction if there were 0.04 mol of product in the solution. 12.95 kJ/mol -12951.75 kJ/mol -12.95 kJ/mol 7.72 kJ/mol
12.95 kJ/mol
Calculate the heat lost from a reaction if the mass of the solution is 18.7 g at a specific heat of 5.008 J/g°C and a change in temperature of 7.2°C. 674.27 J -674.27 J -67.42 J 67.42 J
-674.27 J
Enthalpy is denoted by the _____ symbol. H J ΔE F
H