Flames, Heat, and Calories: An Introduction to Thermodynamics Chapter Pre-lab Qu
ID: 962744 • Letter: F
Question
Flames, Heat, and Calories: An Introduction to Thermodynamics Chapter Pre-lab Questions Make sure you can answer these before you enter the lab! 1. Describe how the flame of a properly adjusted Bunsen burner should appear. 2. Distinguish between heat and temperature. 3. In the melting of ice portion of this experiment, suppose you had 101.2 grams of water which cooled down by 10.2 C upon the addition of 9.7 grams of ice. The final temperature of the ice/water mixture was 20.0°C. Use this data to calculate the heat of fusion for water. (Remember, consider the temperature of ice to be o.0 c. and remember that heat lost equals heat gained!) In Part II of this experiment, you will measure the heat associated with a burning candle. Does this represent a physical change or a chemical change? Describe the change occurring. 4. 5. Describe what is meant by the specific heat of a substance.Explanation / Answer
1)
Undesirable Characteristics of a Flame
A Bunsen burner flame that is not properly adjusted may interfere with an experiment in a number of ways. A flame that does not contain enough air will not burn all the gas coming out of the burner. This results in a flame that is too cool for most experiments and may produce unsafe levels of gas in the work area. A flame that contains too much air will create an unstable, flickering flame that may go out without warning. In addition to interrupting the experiment, this may also produce unsafe levels of gas.
Color
A perfect flame consists of a narrow plume of pale blue flame. A flame that contains any tint of orange color means that either not enough gas is flowing through the burner or not enough air is being mixed with the gas. An orange flame will not be hot enough for most laboratory purposes. A flame with a bright blue triangle within a pale blue flame is too hot for most experiments, although it may be desirable for specific tasks requiring a great deal of heat.
Steadiness
The flame should be very steady, with no flickering or fluttering. A flame that flickers or flutters may have too much air mixed with the gas and is in danger of going out. The flame should also emerge directly from the nozzle of the burner. If there is a visible space between the nozzle and the bottom of the visible flame, there is too much air in the mixture. A steady flame provides the most uniform level of heat and allows for steady and predictable heating.
Sound
Once the flame is properly adjusted, there should be very little sound. A flame that hisses or roars either has too much air in the mix or has the gas level turned up too high. The flame should hiss only if you are producing a very hot flame -- hotter than desirable for most tasks. The air flow should be reduced until the hissing sound fades. If this causes orange flame to appear, lower the gas flow until the flame returns to a uniform pale blue.
2)
Heat and temperature are related and often confused. More heat usually means a higher temperature.
Heat (symbol: Q) is energy. It is the total amount of energy (both kinetic and potential) possessed by the molecules in a piece of matter. Heat is measured in Joules.
Temperature (symbol: T) is not energy. It relates to the average (kinetic) energy of microscopic motions of a single particle in the system per degree of freedom. It is measured in Kelvin (K), Celsius (C) or Fahrenheit (F).
5)
Specific heat of a substance
the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.
1)
Specific heat
the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.
Heat of fusion
The enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid at constant pressure.
the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.
1)
Specific heat
the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.
Heat of fusion
The enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid at constant pressure.
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