1. Using standard heats of formation, determine ?H for the following reactions. Report your answers to the nearest 0.1 kJ.
Fe2O3(s) + 3H2O(l)2Fe(OH)3(s)
B2O3(g) + 3H2O(l)2H3BO3(s)
I am not sure how to approach this question.
This is just another Hess's law problem. I'm sure your chemistry text has an explanation of Hess's law and some examples. To solve the problem, you would need to look up the standard heats of formation for these compounds, which you would probably find in the appendix of your chemistry text.
2. Estimate the difference between ?Hreaction and ?Ereaction for the combustion of liquid butanol (C4H9OH) in excess O2, at T = 298 K.
I know I am have to use the enthalpy equation, but I am not coming out with the right answer.
Could you show your work? If might be easier for us to spot an error if you show us.
3. A gold coin whose mass is 8.05 g is heated to 131.3oC and then quickly dropped into an ice calorimeter. What mass of ice melts? (The amount of heat in an ice calorimeter is determined from the quantity of ice the melts, knowing that it takes 6.01 kJ of heat to melt exactly one mole of ice.)
I am not sure if I have to use enthalpy equations or heat capacity equations.
Here the equation you know that the coin goes from 131.3
oC to 0
oC, so you can calculate the heat lost by the coin. The heat lost by the coin is equal to the heat gained by the ice. When the ice gains heat, it melts and you would calculate the quantity of ice that melts using the equation:
q = n?H
fuswhere n is the number of moles of ice which melt, and ?H
fus is the "enthalpy of fusion" of ice, which means the amount of heat needed to melt one mole of ice. More on this equation should be in your book.
4. What is the speed (in mile per hour) of a 50.7 kg runner whose kinetic energy is 484 J?
I am using the equation E=mv2/2, but I am not coming out with the right answer.
Can you show your work? Are you sure that your units are correct?
5. It takes 93.0 J of heat to raise the temperature of 7.84 g of tin from 1.84C to 56.6C. What is the molar heat capacity of tin?
I used this equation q= nC* change in tempreture, but I don't know if I have to find the number of moles in tin and what I am suppose to do with the 93.0 J of heat.
For molar heat capacity, you want n to be the number of moles of tin. The C you calculate should have units of J/(mol *
oC)
6. A home swimming pool contains 203 m3 of water. At the beginning of swimming season, the water must be heated from 20.0oC to 30.0oC.
How much energy (in kJ) must be supplied?
kJ
If a natural gas heater supplies this energy with an 82.9 % heat transfer efficiency, how many grams of methane must be burned? (The heat of combustion of methane is -803 kJ/mol.)
g
I am using the molar heat capacity equation but I am still having trouble with it.
What kind of trouble?