When 0.514 g of biphenyl (C12H10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.8 °C to 29.4 °C. Find ΔErxn for the combustion of biphenyl in kJ>mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/°C.

Video transcript

Welcome back everyone. When 0.750 g of bic cyclohexane undergoes combustion in a bomb colorimeter. The temperature rises from 24.9 °C to 30.7 °C determine the in in internal energy of the reaction for the combustion in kilojoules per mole. The heat capacity of the bomb colorimeter determined in a separate experiment is 7.69 kilojoules per degree Celsius. And we are given four answer choices. We want to recall that based on the first law of thermodynamics, the change in internal energy is equal to the heat plus work and essentially work would be equal to zero if the reaction is carried out under constant volume. And this is true because we're using the bomb colorimeter. So essentially we're looking for the heat of this reaction based on the law of energy conservation, the heat of the reaction would be equal to negative heat of the color meer which is expressed as negative colorimeter in this case negative, right? Because we're using the law of energy conservation, but the heat of colorimeter is simply the colorimeter constant multiplied by the change in temperature. And that's all that we need, we're going to use negative 7.69 k jules per degree Celsius. Let's multiply that by the difference between the final temperature and the initial. And now let's know that gives, this gives us kilojoules, but we want to get kilojoules per more. So we also want to incorporate the mass of bicycle hean used. What does that mean? Well, essentially we want to take that number in kilojoules and divide by the number of moles of bicycle hexane used. So now what can we do? Well, essentially we're just going to put a fraction sign, we can immediately notice that we are going to get kilojoules on top, right? Because Celsius will be canceled out and to get moles on the bottom, we have to recall that the number of moles is simply the ratio between mass and molar mass. What is the mass? Well, at 0.750 g. And we want to divide that by the molar mass of bicycle hexane using the periodic table, we can determine that this would be 166.30 g per mole. And now if we perform the calculation, we get negative 9.89 multiplied by 10 to the third kill a jewel for M, we can essentially tell that the correct answer to this problem would be option B negative 9.89 multiplied by 10, the third kilojoules per mole. Thank you for watching.