a) A thermometer is a temperature measuring device and even though there are various types such as the mercury and alcohol they all have the same basic features. A liquid-in-glass thermometer is made up of a bulb, capillary, scale, and an expansion chamber. The scale of a thermometer is added by initially marking two points; the highest and the lowest point. To get the highest point the thermometer is obtained by inserting it in an 100 degrees Celsius water bath while the lowest point is obtained by inserting it in a 0 degrees Celsius ice bath. Calibration enables temperature readings to taken with the two endpoints serving as the basis.
b) i) The ice and steam points in an ungraduated thermometer are referred to as the fixed point with that of ice being the lower fixed point while that of steam is the upper fixed point.
ii) -20+60 = 40
100 degrees = 40 = 20th number.
50 degrees =?
iii) 100 degrees = 40
? = 80 = 200 degrees.
Question 2
a) According to Charles’s law, at constant pressure, the volume of an ideal gas is directly proportional to its absolute temperature which can be proven through an inflated balloon. Fill a balloon with air and wrap a string around it to get a measurement of the length and record it, place the balloon in a hot water bath of known temperature for a few minutes then wrap a string around it and record the measurement. Place the balloon in a cold water bath of known temperature and record the changes in the size of the balloon from time to time.
c) Absolute zero can be defined as the point in which no more heat can be removed from a system which corresponds to 0 K.
d) The value of the triple point of 273.16 K which refers to the state in which the all three phases can coexist at equilibrium.
e) The Celcius scale is a scale that is centered on the melting and boiling points of water under normal atmospheric conditions and calibrated into 100 units.
The Kelvin Scale is a scale that is centered on the molecular energy of water whereby absolute zero is the point at which molecular energy is at its lowest.
f) T(°C) = (T(°F) - 32) × 5/9
T(°C) = (100 - 32) 5/9 = 37.78
T(K) = (T(°F) + 459.67)× 5/9
T(K) = (100 + 459.67) 5/9 = 310.93 K
Question 3
Although heat and temperature are related they are different phenomena. Heat can be regarded as the sum of all the molecular motion that a particular substance measured in joules while temperature is the measure of the molecular or atomic motion in a particular substance measured in degrees. While the value of heat energy is dependent on the speed, mass, and type of material the value of temperature is independent of these and that is the reason why while a large body of water may have more thermal heat it may have the same temperature as a basin of water.
Question 4
a) A hot water radiator heats a room through a combination of various modes of heat transfer namely; conduction, convection, and radiation. The metallic fins of the radiator conduct heat from the hot water passing through them, the conducted heat through infra-red radiation is transferred to the air that comes into contact with the fins. The heated air expands causing it to lose density since the particles move apart making it rise as it is displaced by the cooler and denser air above it giving rise to convection currents. The heated air eventually loses the heat energy and the process is repeated again which eventually results in the whole room being heated.
b) i) Double-glazing the window minimizes heat loss through conduction and convection if the space between the glass sheets is narrow.
ii) By introducing a cavity wall insulation which prevents heat loss through convection.
g) To prevent heat from escaping through the roof loft insulation should be applied which minimizes heat loss through convection.
Question 5
Equation of thermal conductivity
Q/t = kAΔTtQ/d
Thermal conductivity in any object is determined by four factors all which are present in the equation. Q symbolizes the amount of heat transferred in specific amount of time t, A represents the cross-sectional area of the heat transfer material, k is the thermal conductivity constant of the material, d symbolizes the material`s thickness while ΔT represents the temperature difference of the material.
Equation of electrical conductivity
Electrical conductivity of a material is determined by three factors; the quantity of negatively and positively charged atoms represented as nn and np respectively, the charge present in the atoms qn and qp and the mobility of the atoms represented by un and up.
The two equations are similar since both heat and electrical conduction depend on the free electrons present in the material they pass through.
Question 6
a) Q = hAΔT = = 65 kW.
b) q = Therefore, k = Therefore, k = 1.7 = 0.034 kW/M.K.
Question 7
a) i) Specific heat capacity (c) is the amount of heat (Q) that is required to increase the temperature (θ) of a unit mass by one degree Celsius without changing the state of the material.
ii) Latent heat of fusion can be defined as the amount of heat that gets absorbed as a substance changes its state from solid to liquid and liquid to solid without a change in the temperature.
iii) Latent heat of vaporization can be defined as the amount of heat absorbed by a liquid when it is changing its state into a gas or the amount of heat that a gas needs to lose to change its state into a liquid without a change in temperature.
b) Heat given is equal to heat taken Therefore,
Q1
= McΔT = Q2 = McΔT
Q = 1 1.6 63 = 100.8 KJkg-1
100.8 = 1L
L = = 100.8 KJkg-1. Latent heat of fusion.
100.8 KJ = 1 c 63k
C = = 1.6 Kj Kg-1 K-1. Specific heat capacity.
c) Heat lost by the copper block
Q = McΔT
Q = 100 0.394 -50
Q = -1970 KJ.
Question 9
a) i) Boyle`s law states that at constant temperature, the volume of an ideal gas is inversely proportional to its absolute pressure.
ii) Charles’s law states that at constant pressure, the volume of an ideal gas is directly proportional to its absolute temperature.
iii) Gay-Lussac`s law states that at constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature in Kelvin.
b) The equation of state for an ideal gas is PV = nRT where; P is the pressure, V is the volume, T the absolute temperature, n the number of moles of gas (mass/molar mass) and R is the universal gas constant (8.314 J mol-1 K-1).
Question 10
P1V = nRT1 and P2V = nRT2 Therefore, P1 / P2 = T1
/ T2. Therefore, P2 = P1 T2 T1
P2 = = 1.5 105 pa.
Question 11
PV = nRT. Therefore, n =
n = = 0.005 mol.
Question 12
a) In the equation of the first law of thermodynamics, ΔU represents the change in internal energy of the system, Q represents the net heat that is transferred into the system while W is the net work done by the system.
b) Under the conservation of energy law energy cannot be created or destroyed it can only be redistributed or changed from on form to the other. Therefore, any change in the energy contained within a system is due to the heat that flows across its boundaries and the work done on the system by the surroundings. According to the conservation of energy law only heat and work can lead to a change in the energy contained in a system. This implies that since both can be quantified the change in energy of a system is equal to the sum of the heat inflows and the work done on the system which can be referred as the energy inflows.
Question 13
a) PVy = Constant
101 21.4 = 266.54
Therefore, P2V2y = 266.54
P = = 266.54 kpa.
T1VY = Constant
15 21.4 = 39.59
Therefore, T2V2y
= 39.59
T2 = = 39.59
b) i) Heat exchanged
ΔU = Q + W
ΔU is constant therefore, Q = W
W = 140 joules therefore, Q = 140 joules
ii) Heat absorbed + Heat absorbed during compression = Work done during expansion
140 + 162 = 302 joules.
