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fandomhigh2006-01-26 09:24 am
equalsmcsquared.livejournal.com) wrote in fandomhigh2006-01-26 09:24 am
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Chemistry (4th Period)
"Good morning. I hope you all have been studying the handouts I gave over Dalton's law. Today, we will be doing a series of calculations."
Calculations with Dalton's Law:
Let's try that last experiment with real numbers. In our lab, the atmospheric pressure is 102.4 kPa. The temperature of our water is 25°C. We used a 250 mL beaker instead of a test tube to collect the hydrogen. Let's find the pressure of the hydrogen, and then find the moles of hydrogen using the ideal gas law.
Step 1: We need to know the vapor pressure of the water. A common table lists the pressure at 25°C as 23.76 torr. A torr is 1 mm of mercury at standard temperature. In kilopascals, that would be 3.17 (1 mm mercury = 7.5 kPa). We should also convert the 250 mL to .250 L and 25°C to 298 L.
Step 2: We can use Dalton's Law to find the hydrogen pressure. It would be:
PTotal = PWater + PHydrogen
102.4 kPa = 3.17 kPa + PHydrogen
So the pressure of Hydrogen would be: 99.23 kPa or 99.2 kPa.
Step 3: We use the Ideal Gas Law to get the moles. Recall that the Ideal Gas Law is:
PV=nRT
where P is pressure, V is volume, n is moles, R is the Ideal Gas Constant (0.0821 L-atm/mol-K or 8.31 L-kPa/mol-K), and T is temperature.
Therefore, our equation would be:
99.2 kPa x .250 L = n x 8.31 L-kPa/mol-K x 298 K
This can be re-arranged so:
n = 99.2 kPa x .250 L / 8.31 L-kPa/mol-K / 298 K
n = .0100 mol or 1.00 x 10-2 mol Hydrogen
Another important contribution by John Dalton was his generalization that all gases expand equally on going to the same higher temperature.
Calculations with Dalton's Law:
Let's try that last experiment with real numbers. In our lab, the atmospheric pressure is 102.4 kPa. The temperature of our water is 25°C. We used a 250 mL beaker instead of a test tube to collect the hydrogen. Let's find the pressure of the hydrogen, and then find the moles of hydrogen using the ideal gas law.
Step 1: We need to know the vapor pressure of the water. A common table lists the pressure at 25°C as 23.76 torr. A torr is 1 mm of mercury at standard temperature. In kilopascals, that would be 3.17 (1 mm mercury = 7.5 kPa). We should also convert the 250 mL to .250 L and 25°C to 298 L.
Step 2: We can use Dalton's Law to find the hydrogen pressure. It would be:
PTotal = PWater + PHydrogen
102.4 kPa = 3.17 kPa + PHydrogen
So the pressure of Hydrogen would be: 99.23 kPa or 99.2 kPa.
Step 3: We use the Ideal Gas Law to get the moles. Recall that the Ideal Gas Law is:
PV=nRT
where P is pressure, V is volume, n is moles, R is the Ideal Gas Constant (0.0821 L-atm/mol-K or 8.31 L-kPa/mol-K), and T is temperature.
Therefore, our equation would be:
99.2 kPa x .250 L = n x 8.31 L-kPa/mol-K x 298 K
This can be re-arranged so:
n = 99.2 kPa x .250 L / 8.31 L-kPa/mol-K / 298 K
n = .0100 mol or 1.00 x 10-2 mol Hydrogen
Another important contribution by John Dalton was his generalization that all gases expand equally on going to the same higher temperature.