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level: Level 1

Questions and Answers List

level questions: Level 1

Question	Answer
- all matter (s/l/g) is made up of small particles, atoms or molecules - All particles are in constant motion - No kinetic energy is gained or lost during collisions between particles - there are forces of attraction and repulsion between particles within a material - the distance between particles in a gas are large compared to the size of the particles	Kinetic Particle Model Assumptions
Measures in Joules (J) The transfer of thermal energy from a hotter body to a colder one.	Heat
All particles contain both kinetic and potential energy, the sum of the energies of these particles is the internal energy. As a substance is heated the internal energy within a substance changes.	Internal energy
Measured in degrees Celsius (°C) or in Kelvin (K). A measure of the average kinetic energy of the particles within a substance the faster particles move, the higher the temperature. Increase in kinetic energy = change in temperature.	Temperature
When increasing the internal energy only results in an increase in potential energy, the temperature does not change but the substance changes state.	Increasing internal energy
The increase in internal energy is not used to speed up the particles but is instead used to break the bonds between particles.	Changing State
Absolute scales must not have negative values, zero must be the lowest value. Celsius is an arbitrary scale because it has negative values. Kelvin is an absolute scale because 0 on the Kelvin scale is the temperature at which all movement stops, “zero” kinetic energy.	Arbitrary scales vs. Absolute scales
°C = 273.15K K = -273.15°C	Converting between degrees Celsius and Kelvin
If objects A and B are in thermal equilibrium with object C, then objects A and B are in thermal equilibrium with each other.	The zeroth law of thermodynamics
Thermal contact: energy is able to flow between them. Thermal equilibrium: when two objects in thermal contact stop having a flow of energy between them. Once objects have made thermal contact, they progress towards thermal equilibrium with the “hotter object” the one with more energy, losing energy by transferring it to the “cooler object”, this process will continue until both objects possess the same amount of kinetic energy, and are therefore at the same temperature.	Thermal contact and thermal equilibrium
Any change in the internal energy (ΔU) of a system is equal to the energy added by heating (+Q) or removed by cooling (-Q), minus the work done (-W) or by (+W) the system. ΔU = Q + W	The first law of thermodynamics
1. ΔU = ? Q = -30 kJ W = -40 kJ ΔU = 10 kJ 2. ΔU = ? Q = -72kJ W = -12kJ ΔU = -60 kJ	Calculations
3. ΔU = ? Q = -15 W = 35 ΔU = -50 kJ 4. ΔU = 64. Q = ? W = 27 Q = 91 kJ	calculations
The amount of energy that must be transferred to change the temperature of 1 kg of a material by 1 ˚C or 1 K. Q = mcΔT Q = heat transferred (J) m = mass (kg) c = specific heat capacity (J kg-1 K-1) ΔT = change in temperature (K) ΔT = final temperature – initial temperature	Specifc heat capacity
Q = ? m = 135 L = 135 kg c = 4200 J kg-1 K-1 ΔT = 70 – 20 = 50 K Q = mcΔT = 135 x 4200 x 50 = 28 350 000 J= 28 MJ	A hot water tank contains 135 L of water. Initially the water is at 20 ˚C. Calculate the amount of energy that must be transferred to the water to raise the temperature to 70˚C.
Energy needed to change the state of a substance. Q = mL Q = Heat energy (J) m = mass (kg) L = latent heat (J kg-1) Important: When energy is being used to change the state of a substance there is NO change in temperature!	Latent Heat
Q = ? m = 2.5 L = 2.5 kg Lwater = 3.34x10^5 J kg-1 Q = 8.35x10^2 kJ	How much energy must be removed from 2.5 L of water at 0˚C to produce a block of ice at 0 ˚C. Express your answer in kJ.
Q = ? Q = ? m = 50 ml = 50 g = 0.05 kg m = 0.05 kg c = 4180 J kg-1 K-1 L = 22.5 x 10^5 J kg-1 ΔT = 100 -20 = 80 K Q = 16 800 J Q = 112 500 J total Q = 129 300 J	50 ml of water is heated from a room temperature of 20 ˚C to its boiling point at 100 ˚C . It is boiled at this temperature until it is completely evaporated. How much energy in total was required to raise the temperature and boil the water?
Rate of energy used or supplied by or to an object. (How quickly energy is used/made). P = E/t = Q/t P = power (W) E = energy (J) t = time (s)	Power
Comparison between how much energy is actually used by a system. %efficiency = useful energy/total energy x100 %efficiency = energy output/energy input x100	Efficiency
The process by which heat transfers from one place to another without the net movement of particles. It can occur within or between molecules that are in thermal contact. It's most common in solids. 1. Energy transfer through atomic or molecular collisions 2. Thermal transfer by free electrons.	Conduction
The ability of a material to conduct heat. - Nature of the material. High or low thermal conductivity - Temperature difference between two objects - Thickness of the material - Surface area	Thermal conduction
Convection: the process of transferring thermal energy via the movement of particles over a distance. Forms a convection current. Occurs in liquids and gases. Convection currents: the effectiveness is determined by the placement of the heat source. - The temperature difference between two objects. - The surface area exposed to the convective fluid.	Convection and convection currents
YES	Fridges
Radiation: the transfer of heat from one place to another without the movement of particles via electromagnetic radiation. Electromagnetic radiation: travels at the speed of light and is emitted by all objects above 0 K. The wavelength and frequency of lightis determined by the objects internal energy. When colliding with an object its light will be: - partially reflected - partially transmitted OR - partially absorbed – this will transfer thermal energy	Radiation and electromagnetic radiation
- Surface area - Temperature - Type of Radiation (visible, infrared, UV). - Surface colour and texture (White surfaces will absorb visible light poorly, but infrared light well. Matte black surfaces absorb better than shiny light ones).	What determines the rate of radiation?