Consider the reaction, C2H4(g) + H2(g) ® C2H6(g), where DH = – 137 kJ. How many kilojoules are released when 55.3 g of C2H4 reacts?

137 kJ x (55.3/28) = ?

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To calculate the amount of heat released when 55.3 g of C2H4 reacts, we need to use the concept of molar mass and stoichiometry.

Step 1: Calculate the number of moles of C2H4

The molar mass of C2H4 (ethylene) is:
C = 12.01 g/mol
H = 1.01 g/mol
Total molar mass = (2*12.01) + (4*1.01) = 28.05 g/mol

Using the given mass of C2H4:
Number of moles = mass / molar mass = 55.3 g / 28.05 g/mol = 1.97 mol

Step 2: Use stoichiometry to determine the heat released

The balanced chemical equation tells us the stoichiometric ratio of C2H4 to heat released:
C2H4(g) + H2(g) -> C2H6(g)

From the balanced equation, we can see that 1 mol of C2H4 reacts to produce -137 kJ of heat. Therefore,
1.97 mol of C2H4 reacts to produce -137 kJ/mol * 1.97 mol = -269.89 kJ

Step 3: Calculate the final answer

The amount of heat released when 55.3 g of C2H4 reacts is -269.89 kJ.
Since heat is a form of energy, it is always released as a negative value.

To find the number of kilojoules released when 55.3 g of C2H4 reacts, we need to use the concept of stoichiometry and the given enthalpy change (∆H) of the reaction.

To solve this, you need to follow these steps:

Step 1: Write and balance the chemical equation for the reaction.

The balanced equation for the reaction is:
C2H4(g) + H2(g) => C2H6(g)

Step 2: Determine the molar mass of C2H4.

C2H4 has a molar mass of:
(2 * atomic mass of C) + (4 * atomic mass of H)
= (2 * 12.01 g/mol) + (4 * 1.01 g/mol) = 28.05 g/mol

Step 3: Convert the given mass of C2H4 to moles.

To convert grams to moles, use the following formula:
moles = mass / molar mass

moles = 55.3 g / 28.05 g/mol
moles ≈ 1.971 mol

Step 4: Identify the mole ratio between C2H4 and the enthalpy change in the balanced equation.

From the balanced equation, we can see that the mole ratio between C2H4 and the enthalpy change (∆H) is 1:1.

Step 5: Calculate the heat released.

To calculate the heat released, multiply the number of moles of C2H4 by the enthalpy change (∆H).

Heat released = moles of C2H4 * ∆H
= 1.971 mol * (-137 kJ/mol)
≈ -269.23 kJ

The heat released when 55.3 g of C2H4 reacts is approximately -269.23 kJ (Note: The negative sign indicates that the reaction is exothermic).