Heat

Which statement about exothermic reactions is accurate?

As reactants form products, the potential energy decreases.

Which reaction is exothermic?

CH4 + 2O2→CO2 + 2H2O + 891 kJ

The diagram below shows the temperature dropping from 80°C to 20°C. Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?

Kinetic energy decreases as temperature decreases.

A baker touches a pie right after taking it out of the oven. Which statement best explains why the pie feels hot?

Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin.

Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?

One system must have higher kinetic energy than the other system.

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.

Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B?

The average kinetic energy of A is greater than that of B.

Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?

The gas molecules in both containers have the same average kinetic energy.

Iron reacts with oxygen in a chemical hand-warmer. How should this reaction be categorized?

as an exothermic process because it releases heat

In what type of reaction or process does heat flow into the system?

endothermic