reactivity 1.1

Question 1

temperature is the measure of _____

Answer 1

the average kinetic energy of the particles

Question 2

heat is the measure of _____

Answer 2

the energy content of a substance

Question 3

energy is a measure of ______

Answer 3

the ability to do work

Question 4

what can/can’t open systems transfer? x2

Answer 4

can transfer energy AND matter

Question 5

what can/can’t closed systems transfer? x2

Answer 5

can transfer energy BUT not matter

Question 6

what can/can’t isolated systems transfer? x2

Answer 6

can not transfer energy NOR matter

Question 7

inside the reaction vessel is known as ___

Answer 7

the system

Question 8

outside the reaction vessel is known as ___

Answer 8

the surroundings

Question 9

what does the law of conservation of energy state?

Answer 9

that energy is neither created or destroyed so the total energy of a process remains the same

Question 10

define enthalpy

Answer 10

the chemical potential energy of a system/the measurement of energy in a thermodynamic system

Question 11

when does enthalpy change?

Answer 11

when chemical reactions take place, changes in chemical energy take place

Question 12

what symbol is an enthalpy change is represented by?

Answer 12

ΔH

Question 13

an enthalpy change can be _______ or _________

Answer 13

positive or negative

Question 14

what makes a reaction exothermic?

Answer 14

when the products have less enthalpy than the reactants

Question 15

how does temperature in exothermic reactions change in surroundings/system?

Answer 15

heat energy is given off by the system to the surroundings (surroundings temp ↑, system temp ↓)

Question 16

ΔH value in exothermic reactions

Answer 16

negative (because there is an enthalpy decrease)

Question 17

why are exothermic reactions thermodynamically possible?

Answer 17

because Hreactants > Hproducts)

Question 18

if the rate of the an exothermic reaction is too slow, what will happen?

Answer 18

the reaction may not occur, so the reaction becomes kinetically controlled

Question 19

what makes a reaction endothermic?

Answer 19

when the products have more enthalpy than the reactants

Question 20

how does temperature in endothermic reactions change in surroundings/system?

Answer 20

heat energy is absorbed by the system from the surroundings (surroundings temp ↓, system temp ↑)

Question 21

ΔH value in endothermic reactions

Answer 21

positive (because there is an enthalpy increase)

Question 22

“the substances that are reacting” is called ______

Answer 22

the system

Question 23

what does an energy profile show? x3

Answer 23

energies of reactants, transition state(s) AND products of the reaction with time

Question 24

define transition state

Answer 24

a stage during the reaction at which chemical bonds are partially broken and formed

Question 25

is the transition state stable? why or why not?

Answer 25

no, it cannot be isolated and is higher in energy than reactants & products

Question 26

define activation energy (Eₐ)

Answer 26

‘the minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction’ (the energy needed to reach the transition state)

Question 27

between exo and endo thermic reactions, which has a lower activation energy? why?

Answer 27

exothermic because the reactants are closer in energy to the transition state

Question 28

how to determine Eₐ from a drawn energy profile

Answer 28

the energy difference from the energy level of the reactants to the top of the ‘hump’

Question 29

what does the standard enthalpy change for a chemical reaction (ΔH^Ꝋ) refer to?

Answer 29

the heat transferred at constant pressure under standard conditions and states

Question 30

what are the standard conditions for ΔH^Ꝋ x3

Answer 30

pressure = 100 kPa, concentration = 1 mol dm⁻³ (for all solutions) AND each substance is in its standard state (gas/liquid/solid)

Question 31

what is the commonly given temperature for ΔH^Ꝋ?

Answer 31

298 K (25℃)

Question 32

what does Ꝋ signify?

Answer 32

that a reaction has been carried out under standard conditions

Question 33

define standard enthalpy change of reaction (ΔH^Ꝋᵣ), is it for both exo and endothermic reactions?

Answer 33

the enthalpy change when the reactants in the stoichiometric equation react to give the products under standard conditions (BOTH ENDO & EXO)

Question 34

define standard enthalpy change of formation (ΔH^Ꝋf), is it for both exo and endothermic reactions?

Answer 34

the enthalpy change when one mole of a compound is formed from its elements under standard conditions (BOTH ENDO & EXO)

Question 35

define standard enthalpy change of combustion (ΔH^Ꝋc), is it for both exo and endothermic reactions?

Answer 35

the enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions (ONLY EXO)

Question 36

define standard enthalpy change of neutralisation (ΔH^Ꝋneut), is it for both exo and endothermic reactions?

Answer 36

the enthalpy change when one mole of water is formed by reacting an acid and alkali under standard conditions (ONLY EXO)

Question 37

define calorimetry

Answer 37

a technique used to measure changes in enthalpy of chemical reactions

Question 38

examples of what can a calorimeter be made of x3

Answer 38

polystyrene drinking cup, vacuum flask OR metal can

Question 39

define specific heat capacity (c) (of the liquid)

Answer 39

the energy needed to raise the temperature of 1g of a substance by 1K

Question 40

what is the specific heat capacity of water?

Answer 40

4.18 J g⁻¹ K⁻¹

Question 41

how can energy transferred as heat be calculated? what do each of the letters mean & what are their units? x2

Answer 41

q = m∙c∙ΔT q ⇒ heat transferred (J) m ⇒ mass of water (g) c ⇒ specific heat capacity (J g⁻¹ K⁻¹) ΔT ⇒ temperature change (K) ΔH = - Q / n ΔH ⇒ change in enthalpy (kJ mol⁻¹) q ⇒ heat transferred (J) n ⇒ # of moles (mol)

Question 42

two types of calorimetry experiments

Answer 42

enthalpy changes of reactions in a solution AND enthalpy changes of combustion

Question 43

principle of ΔH for reactions in solution

Answer 43

the principle of these calorimetry experiments is to carry out the reaction with an excess of one reagent and measure the temperature change over the course of a few minutes

Question 44

define reagent

Answer 44

a substance or compound added to a system to cause a chemical reaction

Question 45

what assumptions are made for ΔH for reactions in solution? 5

Answer 45

c of the solution is = pure water (4.18 J g⁻¹ K⁻¹), density of solutions = pure water (1g cm⁻³), c is ignored, reaction is complete AND there are negligible heat losses

Question 46

what are temperature correction graphs used for?

Answer 46

for reactions which are not instantaneous, there may be a delay before the maximum temperature is reached

Question 47

for non-instantaneous reactions, why may the true maximum temperature not be reached?

Answer 47

during the delay substances may be losing heat to surroundings

Question 48

steps to making a temperature correction graph x3

Answer 48

1. take temperature reading before adding reactants to get a steady value 2. add second reactant and continue recording temperature & time 3. plot the graph and extend the cooling part of the graph until you intersect the time where the second reactant was added

Question 49

principle of ΔH of combustion experiments

Answer 49

the principle here is to use the heat released by a combustion reaction to increase the heat content of water

Question 50

components of a typical & simple calorimeter used to measure the temperature changes to the water (in an ΔH of combustion experiment) x6

Answer 50

insulating lid, water, copper cam, thermometer, draught/draft shield AND spirit burner

Question 51

where can some of the heat produced by the ΔH of combustion reaction escape to (not being transferred to the water)? x2

Answer 51

surroundings AND absorbed by calorimeter

Question 52

ways to minimize heat losses in a calorimeter measuring temperature changes to the water (ΔH of combustion) x3

Answer 52

copper calorimeter should not be too far above the flame, lid placed overtop AND draught/draft shields to block any air currents

Question 53

main sources of error in ΔH of combustion calorimeter experiments x2

Answer 53

heat losses AND incomplete combustion

Question 54

how is water contained in experiments to determine H changes in solution?

Answer 54

in an insulated calorimeter

Question 55

what does a thermochemical equation give?

Answer 55

the equation for the reaction and the corresponding enthalpy change