What conditions are necessary for a heat engine to have an efficiency of 1.0?

Which of the thermodynamic values ($\Delta U$, Q, or W) would be negative for the following systems? the interior of a closed refrigerator (system)

Which of the thermodynamic values ($\Delta U$, Q, or W) would be negative for the following systems? a steel rail (system) undergoing slow thermal expansion on a hot day displaces the spikes and ties that hold the rail in place

A bomb calorimeter is placed in a water bath, and a mixture of fuel and oxygen is burned inside it. The temperature of the water is observed to rise during the combustion reaction. The calorimeter and the water remain at constant volume. If the water bath is the system, which thermodynamic quantities-$\Delta U$, Q, or W-are positive and which are negative?

A bomb calorimeter is placed in a water bath, and a mixture of fuel and oxygen is burned inside it. The temperature of the water is observed to rise during the combustion reaction. The calorimeter and the water remain at constant volume. If the reaction products are the system, which thermodynamic quantities-$\Delta U$, Q, or W-are positive and which are negative?

How do the temperature of combustion and the temperatures of coolant and exhaust affect the efficiency of automobile engines?