topic 4: energetics

Question 1

enthalpy change definition

Answer 1

enthalpy change is the heat energy change measured under conditions of constant temperature.

Question 2

endothermic reaction

Answer 2

-endothermic reactions ABSORBS energy from surroundings
-temperature of surroundings DECREASE
-energy change is POSITIVE
-the enthalpy of the system INCREASES

REACTIONS EXAMPLE: thermal decomposition, photosynthesis

Question 3

exothermic reaction

Answer 3

-exothermic reactions RELEASES energy to the surroundings
-temperature of surroundings INCREASE
-the enthalpy change is NEGATIVE
-the enthalpy of the system DECREASES

REACTIONS EXAMPLE: oxidation, combustion, neutralization

Question 4

standard enthalpy of combustion definition

Answer 4

the enthalpy change when one mole of a substance is completely burned in oxygen with all reactants and products in their standard states under standard condition

Question 5

standard enthalpy of formation definition

Answer 5

the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions, at 298K and 100KPa

Question 6

heat change equation

Answer 6

q=mc△t

Question 7

hess’s law

Answer 7

the overall enthalpy change for a chemical reaction is independent of the route taken from reactants to products

Question 8

mean bond enthalpy definition

Answer 8

The average enthalpy change when one mole of a specified covalent bond is broken, averaged out across the range of compounds.