Chapter 5: Problem 135
Acetylene \(\left(\mathrm{C}_{2} \mathrm{H}_{2}\right)\) can be made by combining calcium carbide \(\left(\mathrm{CaC}_{2}\right)\) with water. (a) Write an equation for the reaction. (b) What is the maximum amount of heat (in joules) that can be obtained from the combustion of acetylene, starting with \(74.6 \mathrm{~g}\) of \(\mathrm{CaC}_{2} ?\)
Short Answer
Step by step solution
Write the Balanced Chemical Equation
Calculate Moles of Calcium Carbide
Combustion of Acetylene
Calculate Heat from Combustion
State the Final Answer
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chemical Reaction Equation
For the production of acetylene using calcium carbide and water, the balanced chemical equation is:\[ \mathrm{CaC}_{2} + 2\mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{C}_{2}\mathrm{H}_{2} + \mathrm{Ca(OH)_{2}}\]
- The reactants include calcium carbide \(\mathrm{CaC}_2\) and water \(\mathrm{H}_2\mathrm{O}\).
- The products are acetylene \(\mathrm{C}_2\mathrm{H}_2\) and calcium hydroxide \(\mathrm{Ca(OH)_2}\).
Moles Calculation
Conversion from mass to moles entails using the molar mass, which is the mass of one mole of a substance. Here's a brief guide on how to calculate:
- Determine the molar mass of the compound (add up the atomic masses of all atoms in the compound).
- Use the formula: \(\text{moles} = \frac{\text{given mass}}{\text{molar mass}}\).
Enthalpy Change
In our case, the combustion equation:\[2 \mathrm{C_{2}H_{2}} + 5 \mathrm{O_{2}} \rightarrow 4 \mathrm{CO_{2}} + 2 \mathrm{H_{2}O}\]shows that the combustion of acetylene has an enthalpy change \(-1300\, \mathrm{kJ/mol}\) of \(\mathrm{C_{2}H_{2}}\). Given 1.164 moles of acetylene (from our moles calculation), the total energy released is:\[ \mathrm{Heat\ released} = 1.164 \times (-1300) = -1512.2\, \mathrm{kJ} = -1512200\, \mathrm{J}\]Converting kilojoules to joules is simple through multiplying by 1000, providing the final heat outcome attained in the reaction. Understanding enthalpy change is essential for energy anticipation in chemical transformations.
Chemical Stoichiometry
For the acetylene combustion reaction:\[ \mathrm{2C_{2}H_{2} + 5O_{2} \rightarrow 4CO_{2} + 2H_{2}O}\]The stoichiometry suggests:
- 2 moles of \(\mathrm{C_{2}H_{2}}\) react with 5 moles of \(\mathrm{O_{2}}\)
- Produce 4 moles of \(\mathrm{CO_{2}}\) and 2 moles of \(\mathrm{H_{2}O}\)