Energetics IB SL
Energetics 5.1
5.1.1
Endothermic: A reaction in which energy is absorbed. If your reactants are at a lower energy level than your products then the reaction is endothermic this means it has a + ΔH°
Exothermic: A reaction in which energy is released. If your reactants are at a higher energy level than your products then the reaction is exothermic this means it has a ΔH°
Standard Enthalpy ( ΔH°) The internal energy stored in the reactants. Only changes in enthalpy can be measured.
1.
When some solid barium hydroxide and solid ammonium thiosulfate were reacted together, the temperature of the surroundings was observed to decrease from 15 ºC to – 4 ºC.
What can be deduced from this observation?
A.
The reaction is exothermic and ∆H is negative.
B.
The reaction is exothermic and ∆H is positive.
C.
The reaction is endothermic and ∆H is negative.
D.
The reaction is endothermic and ∆H is positive.
(Total 1 mark)
5.1.2
Combustion and neutralization are exothermic reactions.
➔
➔
Energetics deals with heat changes in chemical reactions.
Enthalpy is the amount of heat energy contained in a substance. It is stored in the chemical
bonds as a potential energy. When substances react, the difference in the enthalpy between the reactants and products (at constant pressure) results in a heat change which can be measured.
➔ The reaction mixture is called the system and anything around the system is called the
surroundings.
➔ Thermochemical equations give the balanced equation with the enthalpy change.
◆ H₂ (g) + 1/2 O₂ (g) → H₂O (l) ; ∆H°= 286 kJ mol⁻¹
◆ H₂ (g) + 1/2 O₂ (g) → H₂O (g) ; ∆H°= 242 kJ mol⁻¹
● The reason there is a difference in the enthalpy is because the first equation the water produced is in liquid state; this allows through convection currents for the heat to be kept.
➔ In exothermic reactions heat is released to the surroundings.
➔ In
5.1.1
Endothermic: A reaction in which energy is absorbed. If your reactants are at a lower energy level than your products then the reaction is endothermic this means it has a + ΔH°
Exothermic: A reaction in which energy is released. If your reactants are at a higher energy level than your products then the reaction is exothermic this means it has a ΔH°
Standard Enthalpy ( ΔH°) The internal energy stored in the reactants. Only changes in enthalpy can be measured.
1.
When some solid barium hydroxide and solid ammonium thiosulfate were reacted together, the temperature of the surroundings was observed to decrease from 15 ºC to – 4 ºC.
What can be deduced from this observation?
A.
The reaction is exothermic and ∆H is negative.
B.
The reaction is exothermic and ∆H is positive.
C.
The reaction is endothermic and ∆H is negative.
D.
The reaction is endothermic and ∆H is positive.
(Total 1 mark)
5.1.2
Combustion and neutralization are exothermic reactions.
➔
➔
Energetics deals with heat changes in chemical reactions.
Enthalpy is the amount of heat energy contained in a substance. It is stored in the chemical
bonds as a potential energy. When substances react, the difference in the enthalpy between the reactants and products (at constant pressure) results in a heat change which can be measured.
➔ The reaction mixture is called the system and anything around the system is called the
surroundings.
➔ Thermochemical equations give the balanced equation with the enthalpy change.
◆ H₂ (g) + 1/2 O₂ (g) → H₂O (l) ; ∆H°= 286 kJ mol⁻¹
◆ H₂ (g) + 1/2 O₂ (g) → H₂O (g) ; ∆H°= 242 kJ mol⁻¹
● The reason there is a difference in the enthalpy is because the first equation the water produced is in liquid state; this allows through convection currents for the heat to be kept.
➔ In exothermic reactions heat is released to the surroundings.
➔ In