Question

A 20 gram piece of metal is added to a sample of 100 grams of water inside a calorimeter. If the metal is at a temperature of -5° Celsius and the water is at 20° Celsius, which of the following best describes what will occur inside the calorimeter?

Answer 1

The final temperature of the water will be 15° Celsius.

The energy gained by the metal equals the energy lost by the water.

The final temperature of the water will be higher than the initial temperature.

The temperature lost by the water will equal the temperature gained by the metal.

Answer 2

Would I use the calorimetry formula?

Answer 3

When we put the two objects, the metal and water, in thermal contact with each other, then they can effect each others temperature. They do this via heat transfer and, as heat is a form of energy, then an energy exchange will occur until both are at the same temperature. We refer to this as thermal equilibrium, when the water and metal are in thermal contact but are not effecting each other's temperature, as both are at the same.

Naturally, then, the water is at a higher temperature and has higher energy than the metal, so it will give away heat to the metal. It cannot lose any of this heat to its surroundings, as the calorimeter should be insulated. So, its temperature will drop due to the HEAT ENERGY TRANSFER TO THE WATER.

You can't really use the calorimetry formula here, as far as I can see:

Energy gained by metal = Energy lost by water
\[Q metal = Q water\], or
\[mcDeltaT (metal) = mcDeltaT (water)\], if you're familiar with this. We don't know the specific heat capacity of the metal (c (metal)) so we cannot work out the final temperature of the water + metal in thermal equilibrium (delta T = T final - T initial). If you know the values then you can probably work it out, otherwise I'm not sure if the first answer is correct or not.

Answer 4

So would it be D?

Answer 5

heat transfer is always from higher gradient to lower gradient
meaning hot travels to cold and not the other way around

Answer 6

I'm confused :x

Answer 7

what are you confused about
here's a simple thought that we encounter in our daily life
if you left a glass of ice cube on your table, what happens as time goes on?

Answer 8

Don't think so...remember that any energy that the warmer water loses when in thermal contact with the colder metal must go directly to the metal. It cannot go into the surroundings as we are insulated from heat loss to these in the calorimeter. We cannot be sure that the temperatures are the same. Some objects require a lot of heat to raise their temperature whilst some require very little...applying the same heat change to two different objects will not affect their temperatures exactly the same way.

Answer 9

I meant to say above that I don't think the answer is D

Answer 10

It melts.

Answer 11

okay. it melts. now try to posit an explanation why the ice cube melts when you place it on the table and it does not melt if you kept it in the freezer.

Answer 12

Because of the temperature difference. So would it be B because the temperature would be higher than what it was when it first started?

Answer 13

ciaran may be correct here, but we need to calculate if it were true :P

Answer 14

your first sentence is correct. there is a temperature (average heat) difference. let us focus on heat here not the temperature now.

as I have said earlier the heat gradient travels from hot to cold this is always true. that does not merely explain anything and why is so, but just a gross simplification as why ice melts or a metal's temperature from -5 degree celsius to a one (I am not going to tell you how much, this requires a calculation).

Have you studied the term entropy yet or laws of thermodynamics?

Answer 15

I've studied entropy but that is all so far.

Answer 16

these terms: q, deltaH, deltaG, calorie, pressure, volume?

Answer 17

yeah I believe so yes

Answer 18

for simplicity: just accept for now that energy cannot be created nor destroyed. there is always a conservation of energy. So, ciaran is correct to point out that if one energy is lost from a species or 100 g of water, it must've gone somewhere. heat is a form of energy as you may have probably learned. that is what is going on here. The first law of Thermodynamics, which is about the conservation of energy can be used to predict or explain what will happen in the system (metal) and surrounding (water).

Answer 19

@nincompoop yes I was thinking that A could be true but I don't think we are given enough information to work out the final temperature. @yesy7 you might be correct now with B, it's to do with energy transfer from the hotter water to the colder metal, which leads to the metal's temperature rising and water's temperature falling to some final temperature which both share. As we don't know what that is, we cannot really know to much about the exact temperature changes, only energy changes.

Thinking about if you placed ice cubes in a warm glass of water and left them for a while, the ice would begin to melt as it gains heat/energy (both the same thing) from the warmer water. So, the water loses this energy and begins to get cooler. The is kind of what we're talking about here.

Answer 20

I see now, I feel like the real life examples are much more easier to understand for me but I'm going to have to keep studying this because I can't wrap my head around it completely. Thank you both for your help :)

Answer 21

This is nearly more of a Physics question than a Chemistry one...I don't think it's got that much to entrophy

Answer 22

it is a topic covered in both physics and chemistry.

Answer 23

It's a question in my chemistry worksheet...

Answer 24

I have another question if anyone wants to help me but if not thanks again :D

Answer 25

http://www.finedrafts.com/files/CUNY/chemistry/General/Zumdahl%20etal/zuhmdahl%209e/PowerPoint_Lectures/chapter17/