energetics

Question 1

define an exothermic reaction

Answer 1

energy has been given out of the reaction

Question 2

define endothermic reaction

Answer 2

energy has been taken into the reaction

Question 3

give one example of an exothermic reaction

Answer 3

neutralising an acid with an alkali

Question 4

give an example of an endothermic reaction

Answer 4

making white anhydrous copper sulfate and water from blue copper sulfate

Question 5

define enthalpy change

Answer 5

measuring a heat change at a constant pressure

Question 6

what are the standard conditions for measuring enthalpy changes

Answer 6

100 kPa
298 K

Question 7

why are exothermic reactions given a negative sign (-)

Answer 7

the products end up with less heat energy than the reactant as they lost energy when they heated up their surroundings. this means enthalpy change is negative

Question 8

what are energy level diagrams used to show

Answer 8

enthalpy change

Question 9

what is enthalpy change measured in

Answer 9

kJ per mole (mol-1)

Question 10

define enthalpy of formation

Answer 10

the enthalpy change when one mole of substance is formed from its consistuent elements under standard condition, all reactants and products being in their standard states

Question 11

define enthalpy of combustion

Answer 11

the enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states

Question 12

define specific heat capacity

Answer 12

the amount of heat needed to raise the temperature of 1g of substance by 1K

Question 13

what is the equation for calorimetry

Answer 13

Q = mc delta t

Question 14

what is calorimetry used for

Answer 14

to compare the values of enthalpy change for a series of similar compounds because the errors will be similar for every experiment

Question 15

how is a flame calorimeter better than a simple calorimeter

Answer 15

the spiral chimney is made of copper

the flame is enclosed

fuel burns in pure oxygen

Question 16

what is a displacement reaction

Answer 16

a metal that is more reactive than another will displace the less reactive one from a compound

Question 17

how do you minimise the effects of heat lost from a polystyrene cup

Answer 17

plotting a cooling curve

Question 18

define Hess’ law

Answer 18

the enthalpy change for a reaction is the same independent of the route taken from reactants to products

Question 19

define enthalpy change

Answer 19

A heat change at constant pressure

Question 20

what is the difference between heat and temperature

Answer 20

temperature - related to the average kinetic energy of the particles in a system but is independent to the number of particles present

heat- a measure of the total energy of all of the particles present in a given amount of substance and is dependent on the number of particles

Question 21

what are the 3 things you need in order to measure the enthalpy change of a reaction

Answer 21

1. mass of the substance that is being heated up or cooled down
2. temperature change
3. specific heat capacity of the substance

Question 22

what is the equation for enthalpy change

Answer 22

q = mc Δ T

Question 23

why are neutralisation reactions exothermic

Answer 23

they give out heat

Question 24

state the method that allows for heat loss in the enthalpy change practical

Answer 24

• Place 50 cm cubed of 1.0 mol dm-3 hydrochloric acid in a polystyrene cup and 50 cm cubed of 1.0 mol dm-3 sodium hydroxide in another
  2. using a thermometer with 0.1 degrees increments take the temperature of each solution every 30 seconds for 4 minutes to confirm that both solutions remain at the same temperature as the laboratory
  3. Plot a cooling graph and draw a line of best fit through these points
  3. now pour the solution into the other and stir continuously and record the temperature every 30 seconds for 6 minutes