ENERGETICS

Question 1

define endothermic reaction

Answer 1

energy is transferred from surrounding to system requiring heat energy products> energy than reactants = +ve

Question 2

define enthalpy change

Answer 2

heat energy change measured under conditions of constant pressure

Question 3

what are the enthalpy standard conditions

Answer 3

100kpa, 298K, 1 moldm^-3 and all elements in the standard states

Question 4

define standard enthalpy of combustion

Answer 4

enthalpy change that occurs when 1 mol of substance is completely combusted in oxygen under standard states and conditions

Question 5

define standard enthalpy of formation

Answer 5

enthalpy change when 1 mol of compounds is formed with elements under standard states in standard conditions

Question 6

equation for calorimetry

Answer 6

heat change= mass x specific heat capacity x temperature change

Question 7

what errors can be caused by calorimetry

Answer 7

heat loss, incomplete combustion, evaporation, not in standard conditions

Question 8

what does Hess law define

Answer 8

total enthalpy change is independent of the path which the chemical change will take place by

Question 9

define mean bond enthalpy

Answer 9

enthalpy needed to break the covalent bond in gaseous atoms that are arranged over different molecules

Question 10

explain why most collisions do not lead to a reaction

Answer 10

reactions will only occur when collisions will occur with sufficient amount of energy. the energy needed is referred to as the activation energy ( minimum amount of energy). This is the energy needed to break relevant bonds in the reactant molecules.

Question 11

what is mean bond enthalpy

Answer 11

every single bond has a slightly different energy so we use an average value across ranges of compounds containing the bond