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