Question

A chemist measures the energy change ΔH during the following reaction: C3H8 (g) +5O2 (g) →3CO2 (g) +4H2O (l) =ΔH−2220.kJ Use the information to answer the following questions.

This reaction is...

endothermic.

exothermic.

Suppose
81.0g

of
C3H8

react.
Will any heat be released or absorbed?

Yes, absorbed.

Yes, released.

No.

If you said heat will be released or absorbed in the second part of this question, calculate how much heat will be released or absorbed.

kJ

Round your answer to
3

significant digits.

Answer 1

Answer:

The reaction is exothermic.

Yes, released.

The heat released is 4,08x10³ kJ.

Explanation:

For the reaction:

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(l)

The ΔH is -2220 kJ, As ΔH is <0, The reaction is exothermic.

As the reaction is exothermic, the heat of the reaction will be released.

The heat released in 81,0g is:

81,0g C₃H₈×$\frac{1mol}{44,1g}$×$\frac{2220kJ}{1mol}$= 4,08x10³ kJ

-Using molar mass of C₃H₈ to convert mass to moles and knowing that there are released 2220 kJ per mole of C₃H₈-

I hope it helps!

Answer 2

The combustion of C₃H₈ is exothermic, that is, heat is released. The heat released by the combustion of 81.0 g of C₃H₈ is -4.08 × 10³ kJ.

Let's consider the following thermochemical equation.

C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(l)  ΔH = −2220. kJ

By convention, when ΔH < 0, the reaction is exothermic, that is, heat is released.

To calculate the amount of heat released, first, we will convert 81.0 g of C₃H₈ to moles using its molar mass (44.1 g/mol).

$81.0 g \times \frac{1mol}{44.1g} = 1.84 mol$

According to the thermochemical equation, 2220. kJ are released by the combustion of 1 mol of C₃H₈. The heat released by the combustion of 1.84 moles of C₃H₈ is:

$1.84 mol \times \frac{-2220kJ}{mol} = -4.08 \times 10^{3} kJ$

The combustion of C₃H₈ is exothermic, that is, heat is released. The heat released by the combustion of 81.0 g of C₃H₈ is -4.08 × 10³ kJ.

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