Energetics

Question 1

what is heat/ thermal energy

Answer 1

• a form of energy that is transferred from a warmer body to a cooler body
• TOTAL kinetic energy
• heat is a measure of the total energy in a given amount of substance; DEPENDS ON THE SUBSTANCE PRESENT

Question 2

what is temperature

Answer 2

• temperature is a measure of the ‘hotness’ of a substance. It represents the AVERAGE kinetic energy of the substance, but is independent of the amount of substance present

Question 3

what is an endothermic reaction

Answer 3

reaction which absorbs energy (bond breaking)

Question 4

what is an exothermic reaction

Answer 4

reactions which release heat (bond making)

Question 5

what is enthalpy

Answer 5

the heat content of a system; measured in changes

Question 6

what does temperature change depend on

Answer 6

• mass
• heat added
• nature of substance

Question 7

what is specific heat capacity

Answer 7

how much energy is required to raise the temperature of 1 g of a substance

Question 8

what is calorimetry

Answer 8

• how enthalpy change in measured

Question 9

heat equation

Answer 9

q= m x c x dt (Mass x specific heat capacity x temperature change)

Question 10

what is thermochemistry

Answer 10

the study of heat changes that occur during a chemical reaction

Question 11

what is hess law

Answer 11

it states that the enthalpy change for a reaction depends only on the difference between the enthalpy of the products and the enthalpy of the reactions
-regardles of a route of a chemical reaction, the enthalpy change will always be the same

Question 12

what is hess law a statement of

Answer 12

the law of conversation of energy

Question 13

what is the standard enthalpy change of neutralization

Answer 13

the enthalpy change when a STRONG ACID and BASE are reacted together to form ONE MOLE OF WATER under STANDARD conditions (with everything in their standard states)

Question 14

standard enthalpy change of combustion

Answer 14

the enthalpy change when ONE MOLE of a compound is burned in excess OXYGEN under standard conditions

Question 15

standard enthalpy change of formation

Answer 15

enthalpy change when ONE MOLE of the compound is formed in their standard state

Question 16

standard conditions

Answer 16

100 kPa, 298K, solutes with a concentration of 1.00 moldm-3 with the element in its standard form

Question 17

standard state

Answer 17

the most normal, pure and stable state of a substance measured at a pressure of 100 kPa

e.g. carbon: solid graphite, Carbon dioxide= gas

Question 18

what is bond enthalpy

Answer 18

the energy required to break 1 mol of bonds in gaseous covalent molecules under standard conditions
-energy needed to break a bond/energy released when a new bond is formed

Question 19

bond length

Answer 19

as bond length decreases, bond strength increases

Question 20

bond strength

Answer 20

the more bonds, and the shorter the bond length, the stronger

Question 21

bond polarity

Answer 21

• can be described as the difference in the electronegativity of the bonded atoms

Question 22

energy absorbed

Answer 22

bonds broken (endothermic)

Question 23

energy released

Answer 23

bonds made (exothermic)

Question 24

in exothermic reactions, product bond are stronger than…

Answer 24

reactant bonds

Question 25

in endothermic reactions, product bonds are weaker than

Answer 25

reactant bonds

Question 26

why is the ‘average bond enthalpy’ called that

Answer 26

average value as it takes into account the different energies in a bond between the same atoms in different molecules

Question 27

bond that require energy

Answer 27

are endothermic