What is the sign convention of work and heat when it comes to chemical thermodynamics?

The standard enthalpy of combustion at 25°C of hydrogen, cyclohexene (C₆H₁₀) and cyclohexane (C₆H₁₂) are –241, –3800 and –3920 kJ mol–1 respectively. Calculate the standard enthalpy of hydrogenation of cyclohexene.

HCP crystal is made of A ions and B ions are arranged in 2/3rd of octahedral voids. The simplest formula of compound is :-

Enthalpy of neutralisation of CH₃COOH by NaOH is – 50.6 kJ/mol and the heat of neutralisation of a strong acid with NaOH is – 55.9 kJ/mol. The value of ΔH for the ionisation of CH₃COOH is :

Kindly Consider following table–

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Which of the following is a carbonate ore ?