2.1 Thermochemistry

Question 1

What is enthalpy change?

Answer 1

The heat energy change measured under conditions of constant pressure

Question 2

what are standard conditions?

Answer 2

pressure:100kPa
temperature: 298K

Question 3

what is an exothermic reaction?

Answer 3

a reaction that transfers energy to its surroundings

Question 4

what is an endothermic reaction?

Answer 4

a reaction that takes in energy from its surroundings

Question 5

what is the sign of ΔH for endothermic and exothermic reactions?

Answer 5

exothermic: ΔH is -
endothermic: ΔH is +

Question 6

what is the definition of the standard enthalpy change of reaction ΔrH⁰?

Answer 6

the enthalpy change that occurs when the quantities of reactants shown in the equation react under standard conditions, with all reactants and products in their standard states

Question 7

what is the definition of the standard enthalpy change of formation ΔfH⁰?

Answer 7

the enthalpy change when one mole of product is formed from its constituent elements with all reactants and products in their standard states under standard conditions

Question 8

enthalpy change graph (exothermic)

Answer 8

reactant higher than product

Question 9

what is the definition of the standard enthalpy change of combustion ΔcH°?

Answer 9

the enthalpy change that occurs when one mole of compound is completely reacted with excess oxygen under standard conditions with all reactants and products in their standard states

Question 10

enthalpy change graph (endothermic)

Answer 10

product higher than reactant

Question 11

what is the calculation for energy transferred?

Answer 11

q= mcΔt

Question 12

what is the equation for ΔH using q=mcΔt?

Answer 12

ΔH = q / n (n = mols) (q= energy)

Question 13

what is the energy change using graphs calculation?

Answer 13

product - reactant

Question 14

What is Hess’s Law?

Answer 14

The total enthalpy change for a reaction is independent of the route taken.

Question 15

what is meant by bond enthalpy?

Answer 15

the energy needed to break a specific type of covalent bond, averaged out across a wide variety of different compounds

Question 16

what changes can be made in a prac to make it more accurate?

Answer 16

polystyrene cup or add lid to prevent heat loss
measure to 0.1 for greater range

Question 17

which way do arrows point for combustion?

Answer 17

arrows down

Question 18

which way do arrows point for formation?

Answer 18

arrows up

Question 19

definition of mean bond energy

Answer 19

the average energy needed to break a specific type of covalent bond average out across a variety of different gaseous species

Question 20

explain why it is better to use powdered metals than a ribbon of them

Answer 20

powdered has a greater surface area so increases rate of reaction

Question 21

where do you calculate formation?

Answer 21

only in compounds and in elements its always zero

Question 22

Label a spirit burner practical
(enthalpy change of combustion)

Answer 22

• thermometer
  -beaker
  -clamp
  -water in beaker
• spirit burner
• wick in sb
• methanol inside sb

Question 23

label the enthalpy change of reaction practical

Answer 23

-thermometer
-calorimeter

Question 24

why can’t the combustion apparatus be used to determine the enthalpy change of ethene?

Answer 24

ethene is a gas (only works for liquids and solids)