Energetics

Question 1

what is an exothermic reaction?

Answer 1

gives out energy so enthalpy change is negative

Question 2

what is an endothermic reaction?

Answer 2

absorbs energy so enthalpy change is positive

Question 3

what is mean bond enthalpy?

Answer 3

bond enthalpy is energy required to break bonds

so its the average energy needed to break a certain type of bond

Question 4

define standard enthalpy of formation

Answer 4

enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

Question 5

define standard enthalpy of combustion

Answer 5

enthalpy change when 1 mole of a substance is completely burnt in oxygen under standard conditions

Question 6

how do you work out the enthalpy change of a reaction?

Answer 6

bonds broke - bonds formed

Question 7

describe an experiment to calculate the standard enthalpy change of a combustion reaction

Answer 7

calorimetry
heat up a known mass of water
use the temp change, water mass and specific heat capacity of water
heat can be lost to the surroundings

Question 8

describe an experiment to calculate the enthalpy change of a neutralisation reaction

Answer 8

calorimetry
add known mass of acid to insulated container (polystyrene cup) and measure the temp
add known measure of alkali mix and record temp over time

Question 9

what is Hess’ law?

Answer 9

the total enthalpy change of a reaction is independent of the rout taken

Question 10

what is the enthalpy change of formation for any element?

Answer 10

Zero