Chapter 9 Enthalpy changes

Question 1

Law of conservation of energy?

Answer 1

Energy cannot be created or destroyed, only transferred

Question 2

Enthalpy?

Answer 2

Measure of heat energy present in a system

Question 3

What letter represents enthalpy

Answer 3

H

Question 4

Enthalpy change?

Answer 4

Energy released or taken in during a chemical reaction

Question 5

Exothermic reaction?

Answer 5

Reaction which releases energy to the surroundings

Question 6

Is the enthalpy change value for an exothermic reaction pos or neg

Answer 6

Neg

Question 7

Endothermic reaction?

Answer 7

Reaction which takes in energy from the surroundings

Question 8

Is the enthalpy change value of an endothermic reaction pos or neg

Answer 8

Positive

Question 9

Activation energy?

Answer 9

Minimum energy requires for a reaction to take place

Question 10

Symbol for activation energy

Answer 10

E subscript a

Question 11

Why are standard conditions relevant to enthalpy changes

Answer 11

The enthalpy change of a reaction can vary depending on the conditions provided

Question 12

What are the standard condition? 4

Answer 12

100kPa (approx 1atm pressure)
298 K (25°c)
1 mol dm^-3 (relevant for sols)
Standard state

Question 13

what is standard state

Answer 13

The state of a substance under standard conditions e.g H2O is liquid

Question 14

Is RTP the same as standard conditions

Answer 14

No

Question 15

Symbol for standard conditions

Answer 15

circle with a line through

Question 16

Definition for standard enthalpy change of reaction? 3 parts

Answer 16

The enthalpy change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions

Question 17

units for enthalpy change

Answer 17

kJ mol^-1

Question 18

Definition for standard enthalpy change of formation 2parts

Answer 18

The enthalpy change associated with the formation of one mole of a compound from its elements under standard conditions

Question 19

What is the enthalpy change of formation for an element

Answer 19

Zero

Question 20

Definition for standard enthalpy change of combustion

Answer 20

The enthalpy change associated with the complete combustion of one mole of a substance under standard conditions

Question 21

Definition for standard enthalpy change of neutralisation 3 parts

Answer 21

The enthalpy change associated with the formation of one mole of water from a naturalisation reaction between an acid and a base, under standard conditions

Question 22

What iss the value of the enthalpy change of neutralisation for the reaction between a strong acid and base

Answer 22

-57 km mol^-1

Question 23

Is standard enthalpy change of combustion always pos or neg, why?

Answer 23

Always neg bc combustion is an exothermic reaction

Question 24

Why is standard enthalpy change of neutralisation normaly the same value across different reactions?

Answer 24

Bc the same half equation is maintained: one mol of H+, one mol of OH- to form one mol oh H2O

Question 25

Subscript of standard enthalpy change of neutralisation

Answer 25

neut

Question 26

subscript of standard enthalpy change of combustion

Answer 26

c

Question 27

subscript of standard enthalpy change of formation

Answer 27

f

Question 28

subscript of standard enthalpy change of reaction

Answer 28

r

Question 29

symbol for heat energy (Not enthalpy)

Answer 29

q

Question 30

equation for calculating heat energy transferred between a system and its surroundings

Answer 30

q=mc delta T

Question 31

unit for specific heat capacity (c)

Answer 31

J g^-1 K^-1

Question 32

Unit for temp

Answer 32

Kelvin

Question 33

how can we more accurately calculate change in temp experimentally

Answer 33

with a cooling curve extrapolation

Question 34

Hiw do you produce a cooling curve extrapolation

Answer 34

Take temp of sol at short, regular intervals Add other reactant to sol Record temp of reaction mixture at regular intervals Plot a cooling curve Extrapolate the line of best fit and draw a line up from the x axis front he time the reactants were added to the sol The crossing point of the 2 lines is the max temp

Question 35

what is the function of a cooling curve extrapolation

Answer 35

corrects for heat loss during the experiment