3.a - Energetics

Question 1

definition of exothermic reaction

Answer 1

chemical reaction in which heat energy is given out

Question 2

definition of endothermic reaction

Answer 2

chemical reaction in which heat energy is taken in

Question 3

definition of calorimetry experiment

Answer 3

allows you to measure the amount of energy transferred in a chemical reaction

Question 4

describe combustion calorimetry experiment

simple terms

Answer 4

measure amount of energy transferred when fuel is burnt

burn the fuel + use flame to heat up some water

uses metal container made out of copper ( conducts heat well )

Question 5

describe the steps for a combustion calorimetry

full terms ) ??? ( need to check accuracy with teacher

Answer 5

1. cold water ( 50cm3 or g) measured into a copper calorimeter ( small metal can )
2. starting temp of water recorded
3. water heated using flame from burning fuel
4. final temp of water is recorded

Question 6

describe the steps of dissolving, displacement + neutralisation calorimetry reactions

Answer 6

take the temp of the reactants ( make sure they are the same ) mix them in a polystyrene cup and measure the temp of the solution at the end

can educe energy lost to surrounding by placing polystyrene cup into a beaker of cotton wool to give more insulation + put lid on cup to reduce energy lost by evaporation

Question 7

what is the equation for heat energy change/ transferred ( Q )

Answer 7

Q = mc /\ T

Heat energy transferred ( J ) = mass of liquid being heated (g ) x specific heat capacity ( J/g/*C) x change in temp of liquid

Question 8

how do you calculate molar enthalpy change from ( /\ H ) from heat energy change ( Q )

Answer 8

1. calculate heat energy change ( Q )
2. find how many moles of fuel ( produced this energy change )
3. molar enthalpy = Q / moles

either have a + / - depending on if reaction is endothermic or exothermic

Question 9

PAPER 2

be able to draw and explain energy level diagrams to represent exothermic and endothermic reactions

Answer 9

???

Question 10

PAPER 2

definition of Bendo Mex

Answer 10

B reaking bonds is ENDOthermic

M aking bonds is EXothermic

Question 11

PAPER 2

be able to use bond energies to calculate enthalpy change during a chemical reaction

Answer 11

???

enthalpy change ( /\H ) = total energy absorbed to break bonds - total energy released in making bonds

Question 12

PAPER 2

what does a positive ( + ) energy change mean

Answer 12

endothermic

Question 13

PAPER 2

what does a negative ( - ) energy change mean

Answer 13

exothermic