Unit 1B : Heat

Which direction does thermal energy flow in the following diagram?

• Heat flows from the ice cream to the hand.

• Heat flows from the hand to the ice cream.

• The system is in a state of equilibrium.

• The system is too cold for heat to move.

Which reaction is endothermic?

• HCl + NaOH --> NaCl + H2O + 58 kJ

• 2C2H6 + 7O2 --> 4CO2 + 6H2O + 2,502 kJ

• 2Na + Cl2 --> 2NaCl + energy

• 6CO2 + 12H2O + energy --> C6H12O6 + 6O2 + 6H2O

How should the baking of a pizza be categorized?

• as an exothermic process because the dough releases heat

• as an exothermic process because the dough absorbs heat

• as an endothermic process because the dough releases heat

• as an endothermic process because the dough absorbs heat

Which statement best describes the direction of heat flow by conduction between two samples of the same material?

• Heat flows from faster molecules to slower molecules when they are near.

• Heat flows from slower molecules to faster molecules when they are near.

• Heat flows from slower molecules to faster molecules when they collide.

• Heat flows from faster molecules to slower molecules when they collide.

How does heat differ from temperature?

• Temperature and heat are the same thing.

• Temperature measures thermal energy, and heat is the flow of thermal energy.

• Temperature measures the loss of energy, and heat measures the gain of energy.

• Temperature is the measure of heat.

Two cups of coffee, one that is at 10°C and one that is at 20°C, are mixed. Which statement about the temperature of the mixture is correct?

• Energy transfer occurs as the molecules collide, and the result is additive; the final temperature is 30°C.

• Energy is transferred from faster moving molecules to slower moving molecules, and the result is the average of 15°C.

• The kinetic theory dictates that the temperature of the coffee in the cooler cup is the final temperature.

• There is no kinetic energy transfer so the temperature of the coffee in the warmer cup is the final temperature.

The diagram below shows the temperature dropping from 80°C to 20°C.

• Kinetic energy decreases as temperature decreases.

• Temperature is not related to the average kinetic energy of a system.

• Molecules vibrate more as temperature decreases.

• There is no change in average kinetic energy between these two systems.

The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?

• The average kinetic energy increases, and the particles collide more frequently.

• The average kinetic energy decreases, and the particles stop colliding.

• The average kinetic energy decreases, and the particles collide less frequently.

• The average kinetic energy increases, and the particles stop colliding.

What is thermal energy?

• the kinetic energy of particles in a system

• the total number of molecules in a system

• the measure of temperature in a system

• the average overall volume of a system

A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?

• Molecules in the skin are moving faster than molecules in the cake.

• The kinetic energy of molecules in the cake is more than the energy in the baking tray.

• Molecules in the cake are moving faster than molecules in the skin.

• The kinetic energy of molecules in the baking tray is more than the energy in the cake.