The reaction between 0.045 g of calcium with an excess of water was carried out in an ice calorimeter as used in this lab. The volume of water in the calorimeter decreased by 0.18 mL during the reaction
a) Write the equation for the reaction which occurs. Is it a redox reaction?
b) Calculate the enthalpy of the reaction (in kJ/mol). Show all steps of calculation.
i got the a), but i need help with b)
what's the enthalpy of formation for calcium hydroxide? wat is it measured in? and what equation do i use?
Please look at your post and look at the material you used to make the post. Is there no temperature listed?
nope...temperature is not given
m = deltaV x (-11.05) is given
i think your're supposed to use this formula to find mass and then use q = m x (deltaHf) to find q
finally u would use deltaH = q/n to find change in enthalpy
im not sure though...and if this is the case, what would be the enthalpy of formation and what is it measured in? kJ/mol or just kJ?
To calculate the enthalpy of the reaction, we need to use the concept of heat exchange and the mass and temperature changes observed during the reaction. Here are the steps to calculate the enthalpy of the reaction:
Step 1: Determine the heat gained or lost by the water in the calorimeter.
The heat gained or lost by the water in the calorimeter can be calculated using the formula:
q = m * C * ΔT
Where:
- q is the heat gained or lost (in J)
- m is the mass of water (in grams)
- C is the specific heat capacity of water (4.18 J/g°C, assuming the density of water is 1 g/mL)
- ΔT is the change in temperature (in °C)
In this case, we know the volume change (0.18 mL), and we can calculate the corresponding mass change using the density of water (1 g/mL).
Mass change = volume change * density of water = 0.18 g
Step 2: Calculate the change in temperature.
Since the reaction took place in an ice calorimeter, we assume the temperature change is equal to the temperature change of the ice, which is 0°C.
ΔT = final temperature - initial temperature = 0°C - (-10°C) = 10°C
Step 3: Calculate the heat exchanged by the water.
q = m * C * ΔT
q = (0.18 g) * (4.18 J/g°C) * (10°C) = 7.524 J
Step 4: Convert joules to kilojoules.
Since the enthalpy of a reaction is typically expressed in kilojoules per mole, we need to convert the joules obtained in the previous step to kilojoules by dividing by 1000.
q = 7.524 J = 7.524 / 1000 kJ = 0.007524 kJ
Step 5: Determine the number of moles of calcium reacted.
To do this, we need to convert the mass of calcium given (0.045 g) to moles using the molar mass of calcium.
Molar mass of calcium = 40.08 g/mol
Number of moles of calcium = mass of calcium / molar mass of calcium
Number of moles of calcium = 0.045 g / 40.08 g/mol ≈ 0.00112 mol
Step 6: Calculate the enthalpy change per mole of calcium reacted.
To determine the enthalpy change per mole of calcium reacted, we can divide the heat exchanged (q) by the number of moles of calcium.
Enthalpy change (ΔH) = q / number of moles of calcium
ΔH = 0.007524 kJ / 0.00112 mol ≈ 6.713 kJ/mol
Step 7: Account for stoichiometry (if required).
If the reaction is balanced and there is one mole of calcium reacting with one mole of water to form calcium hydroxide, then the enthalpy change obtained in Step 6 is the enthalpy change per mole of calcium hydroxide formed.
So, the enthalpy change (ΔH) for the reaction between calcium and water, assuming one mole of calcium reacting with one mole of water, is approximately 6.713 kJ/mol.
To find out the enthalpy of formation for calcium hydroxide (Ca(OH)2), you can consult a reliable reference such as a chemistry textbook or online databases like NIST Chemistry WebBook. The enthalpy of formation is usually measured at standard conditions (25°C and 1 atm) and given in kilojoules per mole (kJ/mol).