For this homework, the concept of “Density” and “Heat” will be explored. Density

Question

For this homework, the concept of “Density” and “Heat” will be explored.

Density is the “compactness” of a material, or stated in a formula it is how much it weighs (mass) divided by how much space it takes up (volume). For pure water the density is 1 gram for every milliliter of water (1 g/ml). From the table below, determine what elements are described in Questions 1-3.

Name of element

Density (g/ml)

Magnesium

1.74

Silicon

2.33

Bismuth

9.80

Zinc

7.14

Sodium

0.97

Boron

2.34

Item weighs 25 grams and takes up 3.5 ml of volume ____Zinc___ (1 pt)

Item weighs 117 grams and takes up 50 ml of volume ___Boron___ (1 pt)

This item floats on water ____Sodium____ (1 pt)

If all these items were mixed together, which one is expected to sink to the bottom? Bismuth__ (1 pt)

“Heat” is the next topic. It is a somewhat difficult concept to grasp but it is very important. I encourage you first to read Chapter 5. Then carefully study the next figure. This figure is a graph that plots temperature over thermal energy. To answer questions 9-12 you need to read, use this graph. No formula is needed!

There are two general types of heat; “Sensible” and “Latent.” Sensible Heat describes a process where the temperature changes as heat is added or removed. Latent Heat Thermal Energy is absorbed but the temperature does not change, for example between points D and C shown in the graph.

The definition of “Heat Capacity” plays a significant role in sensible heat; it is the ability of a substance to store heat. For pure water, the heat capacity is 1 cal / g °C (1 calorie per every gram of water per every degree change in Celsius), or in words; if I have 1 gram of water and I want to raise it 1°C, I must add 1 Calorie of heat. Determine the following:

If I want to raise 2 grams of water 1°C, how much heat should I add? _____________ (1 pt)

If I want to raise 1 gram of water 2°C, how much heat should I add? _____________ (1 pt)

The higher the ‘heat capacity’ of an object, the more heat it takes to increase its temperature. Determine the following:

Wood has 4 times the heat capacity as steel. If I add the same amount of heat to the same amount of steel and wood, I find the temperature of the steel increases to 40°C. What is the temperature of the wood? ___________ (1 pt)

Water has 5 times the heat capacity as soil. If I add the same amount of heat to the same amount of water and soil, I find the temperature of the soil increases to 50°C. What is the temperature of the water? _________ (1 pt).

The next concept to be considered when dealing with heat, is “Latent Heat”. The word latent refers to the temperature of the system remaining the same even as heat is being added or subtracted from it. This will occur when the system is changing states. Consider a piece of ice.

The latent heat of fusion (or the amount of heat required to turn the ice into water) is 80 Calories/gram. How much heat must be added to melt 2 grams of ice at 0°C and what is the final temperature after this heat is added? _______________   _______________ (3 pts)

The latent heat of vaporization (or the amount of heat required to turn the water into a vapor) is 540 Calories/gram. How much heat must be added to turn 3 grams of water at 100°C into a vapor and what will be the final temperature after this much heat is added? _____________   _____________ (3 pts)

Putting sensible and latent heat together, it is now possible to figure out the temperature of water going through various stages of heat input/withdrawal. (Heat capacity of water is 1 cal / g °C)

60 calories is added to 1 gram of water at an initial temperature of 80°C. What is the water’s final temperature and state (solid, liquid or vapor)?

Temperature = __________________ (2 pts)

State = ________________________ (1 pt)

120 calories is removed from 1 gram of water at an initial temperature of 40°C. What is the water’s final temperature and state (solid, liquid or vapor)?

Temperature = __________________ (2 pts)

State = ________________________ (1 pt)

140 Latent heat of vaporization (540 cal/gram) 120 100 Latent heat of O 80 fusion (80 cal/ S 60 gram) Liquid 40 A water 20 D 20 Ce 40 400 600 20 100 200 Heat (calories/gram) 2007 Thomson Higher Education Water vapor 780 800

Explanation / Answer

If weight is 25grams and volume is 3.5ml,density=25/3.5=7.14=ZINC

If weight is 117grams and volume is 50ml,density=117/50=2.34=BORON

The item which floats on water=SODIUM as it has the least density=0.97g/ml

When all are mixed together,the item which sinks is BISMUTH as it has highest density=9.80g/ml

For 2grams of water at 1degree C,0.5 calorie of heat is required(0.5*2=1)

For 1gram of water at 2degree C,2 calories of heat is required(2*1=2)

Wood=4(heat capacity of steel)

Steel=40degree C

Wood=40*4=160degree C

Water=5(heat capacity of soil)

Soil=50degree C

Water=50*5=250degree C

This involves the concept of latent heat were ice changes to water.

80calories is required for a gram and for 2grams,160calories are required.

The final temperature remains the same -0 degree C

This also involves concept of latent heat and for one gram 540calories is required and hence for 3grams,540*3=1620calories is required at 100degree C and final temperature will also be equal to 100degree C.

When 60calories of heat is added at 80degree C,the water would turn up into vapor and final temperature would be 80degree C.

When 120calories is removed from 1gram at 40degree C,the temperature would be 40degree C and state would be solid-ice.

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