[nugiboy]

Hi. I'm a bit stuck on these two questions and could use some help.

1. A vessel and its contents of a total heat capacity 150kJk^-1 were heated using a propane burner. Calculate the maximum theoretical temperature rise when 7g of propane was completely burned. The standard enthalpy of combustion of propane is -2202kJ mol^-1.

I got quite far on this, but am stuck near the end. By knowing the standard enthalpy of combustion of propane is -2202kJ mol^-1, i worked out the enthalpy of combustion for 7g of propane would be -350 kJ. I then tried to use what i had in the formula:

q = c * m * delta T
where
q = enthalpy change
c = total heat capacity
m = mass of substance heated
delta T = change in temperature

I know all the factors except delta T ( which is ok because I'm trying to find it) and m. I'm not sure what m would be. Any ideas. I think Ive done it right so far, but if not let me know.

2. 75cm³ 1.5M nitric acid at 292K were added to 75cm³ 1.5M potassium hydroxide, also at 292K. After reaction, the temperature of the mixture was 302K. What is the molar enthalpy change?

I worked out that there is 0.1125 moles of each substance added to eachother. I can't work out what to do next. Any suggestions would be good.

Thanks in advanced!

[Yggdrasil]

Hi. I'm a bit stuck on these two questions and could use some help.

1. A vessel and its contents of a total heat capacity 150kJk^-1 were heated using a propane burner. Calculate the maximum theoretical temperature rise when 7g of propane was completely burned. The standard enthalpy of combustion of propane is -2202kJ mol^-1.

I got quite far on this, but am stuck near the end. By knowing the standard enthalpy of combustion of propane is -2202kJ mol^-1, i worked out the enthalpy of combustion for 7g of propane would be -350 kJ. I then tried to use what i had in the formula:

q = c * m * delta T
where
q = enthalpy change
c = total heat capacity
m = mass of substance heated
delta T = change in temperature

I know all the factors except delta T ( which is ok because I'm trying to find it) and m. I'm not sure what m would be. Any ideas. I think Ive done it right so far, but if not let me know.

q = mCΔT applies where C is the specific heat capacity (units of J g^-1 K^-1)

when you are given just the heat capacity (not the specific heat capacity) C has units of J K^-1 and your formula is:

q = CΔT

In other words, the heat capacity that they give you in the problem already takes into account the mass of the calorimeter.

2. 75cm³ 1.5M nitric acid at 292K were added to 75cm³ 1.5M potassium hydroxide, also at 292K. After reaction, the temperature of the mixture was 302K. What is the molar enthalpy change?

I worked out that there is 0.1125 moles of each substance added to eachother. I can't work out what to do next. Any suggestions would be good.

Thanks in advanced!

How much solution do you have?  Assuming that the solution has the same density and heat capacity as water, how much heat would you need to increase the temperature by 10 K?