The flame in a torch used to cut metal is produced by burning acetylene (c2h2) in pure oxygen. assuming the combustion of 1 mole of acetylene releases 1251 kj of heat, what mass of acetylene is needed to cut through a piece of steel if the process requires 20.7 × 104 kj of heat?

The mass of acetylene needed is 4290 g of acetylene.

We can see that 1 mole of acetylene produces 1251 kJ of heat, so we can obtain the number of moles of acetylene required from stoichiometry as follows;

1 mole of acetylene produces 1251 kJ of heat

x moles of acetylene produces 20.7 × 10^4 kJ of heat

x = 1 mole × 20.7 × 10^4 kJ / 1251 kJ

x = 165 moles

Now;

Molar mass of acetylene = 26 g/mol

Mass of acetylene =  165 moles × 26 g/mol

= 4290 g of acetylene

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We need 4.31 kg of acetylene

Explanation:

Step 1: Data given

Combustion of 1 mol acetylene releases 1251 kJ of heat

Molar mass of acetylene = 26.04 g/mol

Step 2: Calculate moles of acetylene

1251kJ /mol * x moles = 20.7 * 10^4 kJ

x moles = 20.7 * 10^4 kJ / 1251 kJ/mol

x moles = 165.47 moles

Step 3: Calculate mass of acetylene

Mass acetylene = moles acetylene * molar mass acetylene

Mass acetylene = 165.47 moles * 26.04 g/mol

Mass acetylene = 4308.8 grams = 4.31 kg of acetylene

We need 4.31 kg of acetylene