Heat and Enthalpy

The equation for the combustion of hydrogen is
2H₂(g)+O₂(g)→2H₂O(g);
ΔH=-484 kJ/mol
The energy released when 2.40 g of hydrogen reacts is

• 145 J
• 290 J
• 145 kJ
• 290 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

When 2.20 g of hydrogen reacts with 16.0 g of oxygen according to the following equation:
2H₂(g)+O₂(g)→2H₂O(g); ΔH=-572 kJ/mol

• 286 kJ of energy is absorbed
• 286 kJ of energy is released
• 572 kJ of energy is absorbed
• 572 kJ of energy is released

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The decomposition of water can be represented by the chemical equation
2H₂O(l)→2H₂(g)+O₂(g)
ΔH=+571.8 kJ/mol
From this equation, it can be concluded that the FORMATION of two moles of liquid water from gaseous hydrogen and oxygen is an

• exothermic process releasing 571.8 kJ of heat energy
• exothermic process releasing 1143.6 kJ of heat energy
• endothermic process absorbing 571.8 kJ of heat energy
• endothermic process absorbing 1143.6 kJ of heat energy

Tags

NGSS.HS-PS1-4

Nitrogen dioxide decomposes as follows.
2NO₂(g)→N₂(g)+2O₂(g); ΔH=-66 kJ/mol
The enthalpy change for the reaction represented by the equation 1/2N₂(g)+O₂(g)→NO₂(g) is

• -66 kJ/mol
• -33 kJ/mol
• +33 kJ/mol
• +66 kJ/mol

Tags

NGSS.HS-PS1-2

NGSS.HS-PS3-1

Consider the reaction:
2NO(g) + O₂(g) →2NO₂(g); ΔH=-114 kJ/mol
The amount of energy released during the complete reaction of 1.00 L of nitrogen monoxide at 0^oC and 101.3 kPa is

• 114 kJ
• -114 kJ
• 2.54 kJ
• -2.54 kJ

Tags

NGSS.HS-PS1-4

When 16.0g of methane reacts with 16.0g of oxygen according to the following equation:
CH₄(g)+2O₂ → CO₂(g) + 2H₂O (g); ΔH=-889 kJ/mol

• 222 kJ of energy is absorbed
• 222 kJ of energy is released
• 445 kJ of energy is absorbed
• 889 kJ of energy is released

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The use of E10 fuel in car engines produces carbon dioxide due to the combustion of octane and ethanol according to the equations:
2C₈H₁₈(l)+25O₂(g)→16CO₂(g)+18H₂O(l)
C₂H₆O(l)+3O₂(g)→ 2CO₂(g)+3H₂O(l) 
In a comparison of the complete combustion of samples of pure octane and pure ethanol, both samples release 2000kJ of energy. The ratio n(CO₂) produced by octane sample : n(CO₂) produced by ethanol sample is closest to

• 1:1
• 1:4
• 4:1
• 8:1

Tags

NGSS.HS-PS1-4

Hydrogen reacts with oxygen to form water according to the thermochemical equation:
H₂(g)+1/2O₂(g)→H₂O(l); ΔH=-286 kJ mol^-1
Hence, ΔH for the equation: 2H₂(g)+O₂(g)→2H₂O(g) is most likely to be

• +572 kJ mol^-1
• -572 kJ mol^-1
• -484 kJ mol^-1
• +484 kJ mol^-1

Tags

NGSS.HS-PS1-4

Consider the following thermochemical equation.
N₂(g)+2O₂(g)→2NO₂(g); ΔH=+67.7 kJ mol^-1
N₂(g)+2O₂(g)→N₂O₄(g); ΔH=+9.7 kJ mol^-1
The enthalpy of reaction for the reaction shown in the equation below would be:
2NO₂(g)→N₂O₄(g)

• -77.4 kJ mol^-1
• -58.0 kJ mol^-1
• +58.0 kJ mol^-1
• +77.4 kJ mol^-1

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the following fuels has the highest energy density (measured in kJ kg^-1)?

• methanol
• ethanol
• 1-propanol
• 2-propanol