Thermal Flashcards
What affects the amount of energy needed to raise the temperature of a substance with a mass of 1 Kg by 1 K?
The amount of heat needed to raise the temperature of a substance (material) depends on:
1- mass:
more mass=more particles=more heat needed to move all particles.
2- Type of material:
heat capacity= how much heat a material absorbs and store.
Great capacity = they absorb a lot of energy (difficult to heat up)
less capacity=they don’t absorb lots of energy (easy to heat up)
3- How much the temperature is raised…obviously!!!
The SHC of water is 4200 J / kg oC
How much does the internal energy increase if 0.5 kg of water is heated by 10 oC?
E = m x c x delta t
= 0.5 x 4200 x 10
= 21000 J
The SHC of aluminium is 880 J / kg oC
How much does the internal energy increase if 1 kg of aluminium is heated by 10 oC?
E = m x c x delta t
= 1 x 880 x 10
= 8800 J
Water has a very high specific heat capacity (4200 J/kg°C). What does this mean?
What would happen if water had a low specific heat capacity?
Water takes a huge amount of energy to heat up, but take a long time to cool down too.
Life would have not evolved, water absorbs the right amount of energy for life to develop.
What is the first law of thermodynamics?
Energy is not lost or gained, just transferred or transformed.
What is the zeroth law?
The Zeroth Law states that if two bodies are in equilibrium with a third body, they are in thermal equilibrium with one another.
What is specific latent heat?
The amount of energy transfer necessary to change the state of 1Kg of a substance with no change in its temperature.
What is specific latent heat of fusion?
The amount of energy transfer necessary to melt 1Kg of a solid at its melting temperature.
What is the specific latent heat of vaporisation?
The amount of energy transfer necessary to change1Kg of a liquid into a gas at its boiling point.
Vaporisation is the process of turning a liquid into a gas (vapour)
Calculate the thermal energy, Q, absorbed when 1.5 kg of paraffin is raised from 15°C to 50°C.
What are the 3 modes of heat transfer?
- Conduction
- Convection
- Radiation
If 48 000 J of heat energy are given off when a 2 kg block of metal cools by 12 oC, what is the specific heat capacity of the metal?
Q=mC∆T
C=Q/m∆T
C=(48 000)/(2 × 12)
C=2000J 〖kg〗^(-1) K^(-1)
How much energy is provided by a 500W (Power) heater in 2mins?
E=P × t
E=500W × 120s
E=60 000J or 60kJ
Calculate the equilibrium temperature when 50g of copper at 150oC is added to 100mL of water at 10oC
Cw=4200J Kg-1 K-1. CCu=385 J Kg-1 K-1.
m_w C_w ∆T_w=m_Cu C_Cu ∆T_Cu
0.1×4200×(T_f-10)=0.05×385×(150-T_f)
420T_f-4200=2887.5-19.25T_f
420T_f+19.25T_f=2887.5+4200
439.25T_f=7087.5
T_f=16.1℃
Calculate the amount of heat required to heat 250g of ice at -15oC to steam at 120oC.
Cice=2110 J Kg-1 K-1. Cw=4200 J Kg-1 K-1. Cst=1996 J Kg-1 K-1. Lf=334kJ kg-1. Lv = 2230kJ kg-1
Q=mC_i ∆T_i+mL_f+mC_w ∆T_w+mL_v+mC_s ∆T_s
Q=0.25×2110×15+0.25×334 000+0.25×4200×100+0.25×2230 000+0.25×1996×20
Q=7912.5+83 500+105 000+557 500+9980
Q=763 892.5J
Q≈770kJ
Convert the following:
a) 25°C to K;
b) -8°C to K;
c) 210 K to °C;
d) 480 K to °C.
a) TK = TC + 273 = 25 + 273 = 298 K c) TC = TK - 273 = 210 - 273 = -63°C
b) TK = TC + 273 = -8 + 273 = 265 K d) TC = TK - 273 = 480 - 273 = 207°C
How much heat transfer is required to thaw a 0.450 kg package of frozen vegetables originally at 0°C if their heat of fusion is the same as that of water?
Q = mLf = (0.450 kg)(334 kJ kg-1) = 150 kJ
How much heat transfer is necessary to raise the temperature of a 0.200 kg piece of ice from −20.0°C to 130°C, including the energy needed for phase changes?
Q = mciceΔT + mLf + mcwaterΔT + mLv + mcsteamΔT = (0.200 kg)(2090 J kg-1 °C-1)(20°C) + (0.200 kg)(3.34 x 105 J kg-1) + (0.200 kg)(4186 J kg-1 °C-1)(100°C) + (0.200 kg)(2.256 x 106 J kg-1) + (0.200 kg)(1520 J kg-1 °C-1)(30°C) = 6.19 x 105 J or 619 kJ
