The granite block transferred <u>4080 J</u> of energy, and the mass of the water is <u>35.8 g</u>.
1. <em>Energy from granite block
</em>
The formula for the heat (<em>q</em>) transferred is
<em>q = mC</em>Δ<em>T</em>
<em>m</em> = 126.1 g; <em>C</em> = 0.795 J·°C⁻¹g⁻¹; Δ<em>T</em> = <em>T</em>_f – <em>T</em>_i = 51.9 °C - 92.6 °C = -40.7 °C
∴ <em>q</em> = 126.1 g × 0.795 J·°C⁻¹g⁻¹ × (-40.7 °C) = -4080 J
The granite block transferred 4080 J.
2. <em>Mass of water
</em>
<em>q = mC</em>Δ<em>T
</em>
<em>m = q</em>/(<em>C</em>Δ<em>T</em>)
<em>q </em>= 4080 J; <em>C</em> = 4.186 J·°C⁻¹g⁻¹; Δ<em>T</em> = <em>T</em>_f – <em>T</em>_i = 51.9 °C – 24.7 °C = 27.2 °C
∴ <em>m</em> = 4080 J/(4.186 J·°C⁻¹g⁻¹ × 27.2 °C) = 35.8 g
The mass of the water is 35.8 g.
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Answer : The standard enthalpy of formation of ethylene is, 51.8 kJ/mole
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The formation reaction of will be,
The intermediate balanced chemical reaction will be,
(1)
(2)
(3)
Now we will reverse the reaction 1, multiply reaction 2 and 3 by 2 then adding all the equations, we get :
(1)
(2)
(3)
The expression for enthalpy of formation of will be,
Therefore, the standard enthalpy of formation of ethylene is, 51.8 kJ/mole
Using accurate measurements, using pure chemicals and performing the reaction under the most ideal conditions is important to get a valuable percent yield.
<h3>How we calculate the percent yield?</h3>
Percent yield of any chemical reaction is define as the ratios of the actual yield to the theoretical yield of the product and multiply by the 100.
To get the high percent yield or actual yield of any reaction, we have to perform the reaction under ideal condition because if we not use the standard condition then we get the low rate of reaction. Reactants should be present in the pure form as impurity make unwanted products and reduce the productivity of main product and accurate amount of reactants also important for the spontaneous reaction.
Hence, options (a), (b) & (c) are correct.
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