chem enthaply change practical

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Miasmarome
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#1
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#1
in decreasing uncertainty in temp change,
mark scheme says to reduce mass of water used.
how does lower mass reduce uncertainity
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TriplexA
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(Original post by Miasmarome)
in decreasing uncertainty in temp change,
mark scheme says to reduce mass of water used.
how does lower mass reduce uncertainity
Hi there.

I could be completely wrong as it's been a while since I did chem but looking at the equation Q= mc delta t

If we decrease m (the mass of water) then we require a greater delta T value as C is constant. By increasing the size of the measurement made we decrease the uncertainty for finding the Temp Change.

aliaa03 or charco if you could just look over this and confirm/correct this if needs be
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Miasmarome
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(Original post by TriplexA)
Hi there.

I could be completely wrong as it's been a while since I did chem but looking at the equation Q= mc delta t

If we decrease m (the mass of water) then we require a greater delta T value as C is constant. By increasing the size of the measurement made we decrease the uncertainty for finding the Temp Change.

aliaa03 or charco if you could just look over this and confirm/correct this if needs be
by decreasing mass of water, how does this result in a larger change in temp?
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aliaa03
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(Original post by TriplexA)
Hi there.

I could be completely wrong as it's been a while since I did chem but looking at the equation Q= mc delta t

If we decrease m (the mass of water) then we require a greater delta T value as C is constant. By increasing the size of the measurement made we decrease the uncertainty for finding the Temp Change.

aliaa03 or charco if you could just look over this and confirm/correct this if needs be
i can’t believe ive been tagged in a chem question !!!

icl though i’m not really sure about the answer 😭 i’m pretty sure your explanation was right though so i’ll leave it here 😂
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Miasmarome
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(Original post by aliaa03)
i can’t believe ive been tagged in a chem question !!!

icl though i’m not really sure about the answer 😭 i’m pretty sure your explanation was right though so i’ll leave it here 😂
yh the explanation seems correct, but can you explain how decreasing mass of water increases temp change
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tony_dolby
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(Original post by Miasmarome)
by decreasing mass of water, how does this result in a larger change in temp?
Let's say you're burning x amount of alcohol and heating a beaker of water with it (a poor experiment but let's leave that for now!). Burning this amount of alcohol x will emit a certain amount of energy Q. This amount of energy will always be the same. However to calculate this energy, Q, we're relying on heating a known mass of water 'm'. We are then going to measure how much the temperature goes up. If Q is always staying the same, then a small value of 'm' will result in a large delta T. We can see this from the Q=mc deltaT equation.

You can also visualise this. Imagine trying to meaure the temperature change resulting from heating a swimming pool of water with a spirit burner. You would need a very accurate and precise thermometer. The uncertainties would be enormous. Much better to heat a beaker of water instead.

I can see your confusion because to reduce uncertainties we normally want numbers to be as big as possible. However, we're not trying to reduce the uncertainty in the mass of water measurement, but in the temperature reading which depends on the mass of water.
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Miasmarome
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#7
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(Original post by tony_dolby)
Let's say you're burning x amount of alcohol and heating a beaker of water with it (a poor experiment but let's leave that for now!). Burning this amount of alcohol x will emit a certain amount of energy Q. This amount of energy will always be the same. However to calculate this energy, Q, we're relying on heating a known mass of water 'm'. We are then going to measure how much the temperature goes up. If Q is always staying the same, then a small value of 'm' will result in a large delta T. We can see this from the Q=mc deltaT equation.

You can also visualise this. Imagine trying to meaure the temperature change resulting from heating a swimming pool of water with a spirit burner. You would need a very accurate and precise thermometer. The uncertainties would be enormous. Much better to heat a beaker of water instead.

I can see your confusion because to reduce uncertainties we normally want numbers to be as big as possible. However, we're not trying to reduce the uncertainty in the mass of water measurement, but in the temperature reading which depends on the mass of water.
thank you soo much, i understand it now
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