energetics

Question 1

define enthalpy

Answer 1

referring to all of the heat energy that is stored in a chemical system.

Question 2

define enthalpy change

Answer 2

the heat energy transferred in a reaction at a constant temperature

Question 3

symbol used to represent the enthalpy (change) and units?

Answer 3

delta H
kJ mol^-1

Question 4

define what is meant by a ‘‘chemical system’’’

Answer 4

all of the therefore chemicals present in the reaction

Question 5

why do refer to the reactions regarding enthalpy as being a change in enthalpy?

Answer 5

overall enthalpy is different to determine

Question 6

an example of a reaction releasing heating energy?

Answer 6

neutralisation reactions

Question 7

how do you calculate the enthalpy change of a substance?

Answer 7

delta H = H - H
delta = change in
delta H (change in enthalpy) = products - reactants

Question 8

define what is meant by exothermic reactions

Answer 8

exothermic reactions give out the heat energy that is being released from the chemical system to the surroundings, so the temperature of the surroundings in the reaction increases

Question 9

whats happening to the enthalpy of the chemical system?

Answer 9

increases then decreases.
the increase is referred to as the activation energy

Question 10

in order for any reaction to take place what must happen?

Answer 10

we start by breaking the chemical bonds in the reactant molecules. Breaking chemical bonds requires energy, it represents the activation energy of the reaction.

Question 11

define what is meant by the activation energy

Answer 11

the minimum amount of energy required for a reaction to therefore take place therefore so as.

Question 12

end result of the exothermic reactions?

Answer 12

the products of the reaction end up with less energy than the reactants. Therefore means the enthalpy change for the reaction, delta H, is therefore to be negative